diff --git a/chrome/content/zotero/overlay.js b/chrome/content/zotero/overlay.js
index 974295e43a..580bba8283 100644
--- a/chrome/content/zotero/overlay.js
+++ b/chrome/content/zotero/overlay.js
@@ -230,7 +230,7 @@ var ZoteroOverlay = new function()
 			
 			// Warn about unsafe data directory on first display
 			let dataDir = Zotero.getZoteroDirectory();
-			Zotero.checkForUnsafeDataDirectory(dataDir.path);
+			Zotero.DataDirectory.checkForUnsafeLocation(dataDir.path); // async
 
 			// Make sure tags splitter isn't missing for people upgrading from <2.0b7
 			document.getElementById('zotero-tags-splitter').collapsed = false;
diff --git a/chrome/content/zotero/preferences/preferences_advanced.js b/chrome/content/zotero/preferences/preferences_advanced.js
index 2afa4d1393..f14084434c 100644
--- a/chrome/content/zotero/preferences/preferences_advanced.js
+++ b/chrome/content/zotero/preferences/preferences_advanced.js
@@ -38,8 +38,8 @@ Zotero_Preferences.Advanced = {
 	
 	
 	migrateDataDirectory: Zotero.Promise.coroutine(function* () {
-		var currentDir = Zotero.getZoteroDirectory().path;
-		var defaultDir = Zotero.getDefaultDataDir();
+		var currentDir = Zotero.DataDirectory.dir;
+		var defaultDir = Zotero.DataDirectory.defaultDir;
 		if (currentDir == defaultDir) {
 			Zotero.debug("Already using default directory");
 			return;
@@ -65,7 +65,7 @@ Zotero_Preferences.Advanced = {
 		);
 		
 		if (index == 0) {
-			yield Zotero.markDataDirectoryForMigration(currentDir);
+			yield Zotero.DataDirectory.markForMigration(currentDir);
 			Zotero.Utilities.Internal.quitZotero(true);
 		}
 	}),
@@ -215,13 +215,13 @@ Zotero_Preferences.Advanced = {
 	onDataDirLoad: function () {
 		var useDataDir = Zotero.Prefs.get('useDataDir');
 		var dataDir = Zotero.Prefs.get('lastDataDir') || Zotero.Prefs.get('dataDir');
-		var defaultDataDir = Zotero.getDefaultDataDir();
-		var currentDir = Zotero.getZoteroDirectory().path;
+		var currentDir = Zotero.DataDirectory.dir;
+		var defaultDataDir = Zotero.DataDirectory.defaultDir;
 		
 		// Change "Use profile directory" label to home directory location unless using profile dir
 		if (useDataDir || currentDir == defaultDataDir) {
 			document.getElementById('default-data-dir').setAttribute(
-				'label', Zotero.getString('dataDir.default', Zotero.getDefaultDataDir())
+				'label', Zotero.getString('dataDir.default', Zotero.DataDirectory.defaultDir)
 			);
 		}
 		
@@ -232,14 +232,14 @@ Zotero_Preferences.Advanced = {
 		
 		document.getElementById('data-dir-path').setAttribute('disabled', !useDataDir);
 		document.getElementById('migrate-data-dir').setAttribute(
-			'hidden', !Zotero.canMigrateDataDirectory()
+			'hidden', !Zotero.DataDirectory.canMigrate()
 		);
 		
 		return useDataDir;
 	},
 	
 	
-	onDataDirUpdate: function (event) {
+	onDataDirUpdate: Zotero.Promise.coroutine(function* (event) {
 		var radiogroup = document.getElementById('data-dir');
 		var useDataDir = Zotero.Prefs.get('useDataDir');
 		var newUseDataDir = radiogroup.selectedIndex == 1;
@@ -250,11 +250,13 @@ Zotero_Preferences.Advanced = {
 		
 		// This call shows a filepicker if needed, forces a restart if required, and does nothing if
 		// cancel was pressed or value hasn't changed
-		Zotero.chooseZoteroDirectory(true, !newUseDataDir, function () {
-			Zotero_Preferences.openURL('https://zotero.org/support/zotero_data');
-		});
+		yield Zotero.DataDirectory.choose(
+			true,
+			!newUseDataDir,
+			() => Zotero_Preferences.openURL('https://zotero.org/support/zotero_data')
+		);
 		radiogroup.selectedIndex = this._usingDefaultDataDir() ? 0 : 1;
-	},
+	}),
 	
 	
 	chooseDataDir: function(event) {
@@ -269,7 +271,7 @@ Zotero_Preferences.Advanced = {
 		var prefValue = Zotero.Prefs.get('lastDataDir') || Zotero.Prefs.get('dataDir');
 		
 		// Don't show path if the default
-		if (prefValue == Zotero.getDefaultDataDir()) {
+		if (prefValue == Zotero.DataDirectory.defaultDir) {
 			return '';
 		}
 		
@@ -285,7 +287,7 @@ Zotero_Preferences.Advanced = {
 		
 		var dataDir = Zotero.Prefs.get('lastDataDir') || Zotero.Prefs.get('dataDir');
 		// Default home directory location
-		if (dataDir == Zotero.getDefaultDataDir()) {
+		if (dataDir == Zotero.DataDirectory.defaultDir) {
 			return true;
 		}
 		
diff --git a/chrome/content/zotero/preferences/preferences_advanced.xul b/chrome/content/zotero/preferences/preferences_advanced.xul
index 5a984a0b36..fabd06535d 100644
--- a/chrome/content/zotero/preferences/preferences_advanced.xul
+++ b/chrome/content/zotero/preferences/preferences_advanced.xul
@@ -185,7 +185,7 @@
 						<radiogroup id="data-dir"
 								preference="pref-useDataDir"
 								onsyncfrompreference="return Zotero_Preferences.Advanced.onDataDirLoad()"
-								onsynctopreference="return Zotero_Preferences.Advanced.onDataDirUpdate(event);">
+								onsynctopreference="Zotero_Preferences.Advanced.onDataDirUpdate(event);">
 							<radio id="default-data-dir" label="&zotero.preferences.dataDir.useProfile;" value="false"/>
 							<hbox>
 								<radio label="&zotero.preferences.dataDir.custom;" value="true"/>
@@ -199,7 +199,7 @@
 						
 						<hbox>
 							<button label="&zotero.preferences.dataDir.reveal;"
-								oncommand="Zotero.revealDataDirectory()"/>
+								oncommand="Zotero.DataDirectory.reveal()"/>
 							<button id="migrate-data-dir" label="&zotero.preferences.dataDir.migrate;"
 								oncommand="Zotero_Preferences.Advanced.migrateDataDirectory()" hidden="true"/>
 						</hbox>
diff --git a/chrome/content/zotero/xpcom/dataDirectory.js b/chrome/content/zotero/xpcom/dataDirectory.js
new file mode 100644
index 0000000000..6545910c8b
--- /dev/null
+++ b/chrome/content/zotero/xpcom/dataDirectory.js
@@ -0,0 +1,847 @@
+/*
+    ***** BEGIN LICENSE BLOCK *****
+    
+    Copyright © 2016 Center for History and New Media
+                     George Mason University, Fairfax, Virginia, USA
+                     http://zotero.org
+    
+    This file is part of Zotero.
+    
+    Zotero is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+    
+    Zotero is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+    
+    You should have received a copy of the GNU Affero General Public License
+    along with Zotero.  If not, see <http://www.gnu.org/licenses/>.
+    
+    ***** END LICENSE BLOCK *****
+*/
+
+"use strict";
+
+Zotero.DataDirectory = {
+	MIGRATION_MARKER: 'migrate-dir',
+	
+	get dir() {
+		if (!this._dir) {
+			throw new Error("Data directory not initialized");
+		}
+		return this._dir;
+	},
+	
+	get defaultDir() {
+		// Use special data directory for tests
+		if (Zotero.test) {
+			return OS.Path.join(OS.Path.dirname(OS.Constants.Path.profileDir), "Zotero");
+		}
+		return OS.Path.join(OS.Constants.Path.homeDir, ZOTERO_CONFIG.CLIENT_NAME);
+	},
+	
+	get legacyDirName() {
+		return ZOTERO_CONFIG.ID;
+	},
+	
+	_dir: null,
+	_warnOnUnsafeLocation: true,
+	
+	
+	init: Zotero.Promise.coroutine(function* () {
+		var file;
+		if (Zotero.Prefs.get('useDataDir')) {
+			let prefVal = Zotero.Prefs.get('dataDir');
+			// Convert old persistent descriptor pref to string path and clear obsolete lastDataDir pref
+			//
+			// persistentDescriptor now appears to return (and parse) a string path anyway on macOS,
+			// which is the only place where it didn't use a string path to begin with, but be explicit
+			// just in case there's some difference.
+			//
+			// A post-Mozilla prefs migration should do this same check, and then this conditional can
+			// be removed.
+			if (Zotero.Prefs.get('lastDataDir')) {
+				let nsIFile;
+				try {
+					nsIFile = Components.classes["@mozilla.org/file/local;1"]
+						.createInstance(Components.interfaces.nsILocalFile);
+					nsIFile.persistentDescriptor = prefVal;
+				}
+				catch (e) {
+					Zotero.debug("Persistent descriptor in extensions.zotero.dataDir did not resolve", 1);
+					e = { name: "NS_ERROR_FILE_NOT_FOUND" };
+					throw e;
+				}
+				// This removes lastDataDir
+				this.set(nsIFile.path);
+				file = nsIFile.path;
+			}
+			else {
+				// If there's a migration marker in this directory and no database, migration was
+				// interrupted before the database could be moved (or moving failed), so use the source
+				// directory specified in the marker file.
+				let migrationMarker = OS.Path.join(prefVal, this.MIGRATION_MARKER);
+				let dbFile = OS.Path.join(prefVal, this.getDatabaseFilename());
+				if ((yield OS.File.exists(migrationMarker)) && !(OS.File.exists(dbFile))) {
+					let contents = yield Zotero.File.getContentsAsync(migrationMarker);
+					try {
+						let { sourceDir } = JSON.parse(contents);
+						file = OS.Path.normalize(sourceDir);
+					}
+					catch (e) {
+						Zotero.logError(e);
+						Zotero.debug(`Invalid marker file:\n\n${contents}`, 1);
+						e = { name: "NS_ERROR_FILE_NOT_FOUND" };
+						throw e;
+					}
+				}
+				else {
+					try {
+						file = OS.Path.normalize(prefVal);
+					}
+					catch (e) {
+						Zotero.logError(e);
+						Zotero.debug(`Invalid path '${prefVal}' in dataDir pref`, 1);
+						e = { name: "NS_ERROR_FILE_NOT_FOUND" };
+						throw e;
+					}
+				}
+			}
+			
+			if (!(yield OS.File.exists(file)) && file != this.defaultDir) {
+				// If set to a legacy directory that doesn't exist, forget about it and just use the
+				// new default location, which will either exist or be created below. The most likely
+				// cause of this is a migration, so don't bother looking in other-app profiles.
+				if (this.isLegacy(file)) {
+					let newDefault = this.defaultDir;
+					Zotero.debug(`Legacy data directory ${file} from pref not found `
+						+ `-- reverting to ${newDefault}`, 1);
+					file = newDefault;
+					this.set(newDefault);
+				}
+				// For other custom directories that don't exist, show not-found dialog
+				else {
+					Zotero.debug("Custom data directory ${file} not found", 1);
+					throw { name: "NS_ERROR_FILE_NOT_FOUND" };
+				}
+			}
+		}
+		else {
+			let dataDir = this.defaultDir;
+			
+			//
+			// TODO: asyncify
+			//
+			
+			// Check for ~/Zotero/zotero.sqlite
+			let dbFile = OS.Path.join(dataDir, this.getDatabaseFilename());
+			if (yield OS.File.exists(dbFile)) {
+				Zotero.debug("Using data directory " + dataDir);
+				this._cache(dataDir);
+				
+				// Set as a custom data directory so that 4.0 uses it
+				this.set(dataDir);
+				
+				return dataDir;
+			}
+			
+			// Check for 'zotero' dir in profile dir
+			let profileSubdir = OS.Path.join(Zotero.Profile.dir, this.legacyDirName);
+			if (yield OS.File.exists(profileSubdir)) {
+				Zotero.debug("Using data directory " + profileSubdir);
+				this._cache(profileSubdir);
+				return profileSubdir;
+			}
+			
+			//
+			// If Standalone and no directory yet, check Firefox directory, or vice versa
+			//
+			let profilesParent = OS.Path.dirname(Zotero.Profile.getOtherAppProfilesDir());
+			Zotero.debug("Looking for existing profile in " + profilesParent);
+			
+			// get default profile
+			var defProfile;
+			try {
+				defProfile = yield Zotero.Profile.getDefaultInProfilesDir(profilesParent);
+			} catch(e) {
+				Zotero.debug("An error occurred locating the Firefox profile; not "+
+					"attempting to migrate from Zotero for Firefox");
+				Zotero.logError(e);
+			}
+			
+			if(defProfile) {
+				// get Zotero directory
+				let profileDir = defProfile[0].path;
+				Zotero.debug("Found default profile at " + profileDir);
+				
+				// copy prefs
+				let prefsFile = OS.Path.join(profileDir, "prefs.js");
+				if (yield OS.File.exists(prefsFile)) {
+					// build sandbox
+					var sandbox = new Components.utils.Sandbox("http://www.example.com/");
+					Components.utils.evalInSandbox(
+						"var prefs = {};"+
+						"function user_pref(key, val) {"+
+							"prefs[key] = val;"+
+						"}"
+					, sandbox);
+					
+					// remove comments
+					var prefsJs = yield Zotero.File.getContentsAsync(prefsFile);
+					prefsJs = prefsJs.replace(/^#[^\r\n]*$/mg, "");
+					
+					// evaluate
+					Components.utils.evalInSandbox(prefsJs, sandbox);
+					var prefs = sandbox.prefs;
+					for(var key in prefs) {
+						if(key.substr(0, ZOTERO_CONFIG.PREF_BRANCH.length) === ZOTERO_CONFIG.PREF_BRANCH
+								&& key !== "extensions.zotero.firstRun2") {
+							Zotero.Prefs.set(key.substr(ZOTERO_CONFIG.PREF_BRANCH.length), prefs[key]);
+						}
+					}
+					
+					// If data directory setting was transferred, use that
+					if (Zotero.Prefs.get('useDataDir')) {
+						return this.init();
+					}
+				}
+				
+				// If there's a data directory in the default profile for the alternative app, use that
+				let zoteroDir = OS.Path.join(profileDir, this.legacyDirName);
+				if (yield OS.File.exists(zoteroDir)) {
+					this.set(zoteroDir);
+					file = zoteroDir;
+				}
+			}
+			
+			if (!file) {
+				file = dataDir;
+			}
+		}
+		
+		Zotero.debug("Using data directory " + file);
+		yield Zotero.File.createDirectoryIfMissingAsync(file);
+		this._cache(file);
+	}),
+	
+	
+	_cache: function (dir) {
+		this._dir = dir;
+	},
+	
+	
+	/**
+	 * @return {Boolean} - True if the directory changed; false otherwise
+	 */
+	set: function (path) {
+		var origPath = Zotero.Prefs.get('dataDir');
+		
+		Zotero.Prefs.set('dataDir', path);
+		// Clear legacy pref
+		Zotero.Prefs.clear('lastDataDir');
+		Zotero.Prefs.set('useDataDir', true);
+		
+		return path != origPath;
+	},
+	
+	
+	choose: Zotero.Promise.coroutine(function* (forceQuitNow, useHomeDir, moreInfoCallback) {
+		var win = Services.wm.getMostRecentWindow('navigator:browser');
+		var ps = Services.prompt;
+		
+		if (useHomeDir) {
+			let changed = this.set(this.defaultDir);
+			if (!changed) {
+				return false;
+			}
+		}
+		else {
+			var nsIFilePicker = Components.interfaces.nsIFilePicker;
+			while (true) {
+				var fp = Components.classes["@mozilla.org/filepicker;1"]
+							.createInstance(nsIFilePicker);
+				fp.init(win, Zotero.getString('dataDir.selectDir'), nsIFilePicker.modeGetFolder);
+				fp.displayDirectory = Zotero.File.pathToFile(this.dir);
+				fp.appendFilters(nsIFilePicker.filterAll);
+				if (fp.show() == nsIFilePicker.returnOK) {
+					var file = fp.file;
+					let dialogText = '';
+					let dialogTitle = '';
+					
+					if (file.path == (Zotero.Prefs.get('lastDataDir') || Zotero.Prefs.get('dataDir'))) {
+						Zotero.debug("Data directory hasn't changed");
+						return false;
+					}
+					
+					// In dropbox folder
+					if (Zotero.File.isDropboxDirectory(file.path)) {
+						dialogTitle = Zotero.getString('general.warning');
+						dialogText = Zotero.getString('dataDir.unsafeLocation.selected.dropbox') + "\n\n"
+								+ Zotero.getString('dataDir.unsafeLocation.selected.useAnyway');
+					}
+					else if (file.directoryEntries.hasMoreElements()) {
+						let dbfile = file.clone();
+						dbfile.append(this.getDatabaseFilename());
+						
+						// Warn if non-empty and no zotero.sqlite
+						if (!dbfile.exists()) {
+							dialogTitle = Zotero.getString('dataDir.selectedDirNonEmpty.title');
+							dialogText = Zotero.getString('dataDir.selectedDirNonEmpty.text');
+						}
+					}
+					// Directory empty
+					else {
+						dialogTitle = Zotero.getString('dataDir.selectedDirEmpty.title');
+						dialogText = Zotero.getString('dataDir.selectedDirEmpty.text', Zotero.appName) + '\n\n'
+								+ Zotero.getString('dataDir.selectedDirEmpty.useNewDir');
+					}
+					// Warning dialog to be displayed
+					if(dialogText !== '') {
+						let buttonFlags = ps.STD_YES_NO_BUTTONS;
+						if (moreInfoCallback) {
+							buttonFlags += ps.BUTTON_POS_2 * ps.BUTTON_TITLE_IS_STRING;
+						}
+						let index = ps.confirmEx(null,
+							dialogTitle,
+							dialogText,
+							buttonFlags,
+							null,
+							null,
+							moreInfoCallback ? Zotero.getString('general.moreInformation') : null,
+							null, {});
+
+						// Not OK -- return to file picker
+						if (index == 1) {
+							continue;
+						}
+						else if (index == 2) {
+							setTimeout(function () {
+								moreInfoCallback();
+							}, 1);
+							return false;
+						}
+					}
+
+					this.set(file.path);
+					
+					break;
+				}
+				else {
+					return false;
+				}
+			}
+		}
+		
+		var buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING);
+		if (!forceQuitNow) {
+			buttonFlags += (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_IS_STRING);
+		}
+		var app = Zotero.appName;
+		var index = ps.confirmEx(null,
+			Zotero.getString('general.restartRequired'),
+			Zotero.getString('general.restartRequiredForChange', app)
+				+ "\n\n" + Zotero.getString('dataDir.moveFilesToNewLocation', app),
+			buttonFlags,
+			Zotero.getString('general.quitApp', app),
+			forceQuitNow ? null : Zotero.getString('general.restartLater'),
+			null, null, {});
+		
+		if (forceQuitNow || index == 0) {
+			Services.startup.quit(Components.interfaces.nsIAppStartup.eAttemptQuit);
+		}
+		
+		return useHomeDir ? true : file;
+	}),
+	
+	
+	forceChange: function (win) {
+		if (!win) {
+			win = Services.wm.getMostRecentWindow('navigator:browser');
+		}
+		var ps = Services.prompt;
+		
+		var nsIFilePicker = Components.interfaces.nsIFilePicker;
+		while (true) {
+			var fp = Components.classes["@mozilla.org/filepicker;1"]
+						.createInstance(nsIFilePicker);
+			fp.init(win, Zotero.getString('dataDir.selectNewDir', Zotero.clientName), nsIFilePicker.modeGetFolder);
+			fp.displayDirectory = Zotero.File.pathToFile(this.dir);
+			fp.appendFilters(nsIFilePicker.filterAll);
+			if (fp.show() == nsIFilePicker.returnOK) {
+				var file = fp.file;
+				
+				if (file.directoryEntries.hasMoreElements()) {
+					ps.alert(null,
+						Zotero.getString('dataDir.mustSelectEmpty.title'),
+						Zotero.getString('dataDir.mustSelectEmpty.text')
+					);
+					continue;
+				}
+				
+				this.set(file.path);
+				
+				return file;
+			} else {
+				return false;
+			}
+		}
+	},
+	
+	
+	checkForUnsafeLocation: Zotero.Promise.coroutine(function* (path) {
+		if (this._warnOnUnsafeLocation && Zotero.File.isDropboxDirectory(path)
+				&& Zotero.Prefs.get('warnOnUnsafeDataDir')) {
+			this._warnOnUnsafeLocation = false;
+			let check = {value: false};
+			let index = Services.prompt.confirmEx(
+				null,
+				Zotero.getString('general.warning'),
+				Zotero.getString('dataDir.unsafeLocation.existing.dropbox') + "\n\n"
+					+ Zotero.getString('dataDir.unsafeLocation.existing.chooseDifferent'),
+				Services.prompt.STD_YES_NO_BUTTONS,
+				null, null, null,
+				Zotero.getString('general.dontShowWarningAgain'),
+				check
+			);
+
+			// Yes - display dialog.
+			if (index == 0) {
+				yield this.choose(true);
+			}
+			if (check.value) {
+				Zotero.Prefs.set('warnOnUnsafeDataDir', false);
+			}
+		}
+	}),
+	
+	
+	isLegacy: function (dir) {
+		// 'zotero'
+		return OS.Path.basename(dir) == this.legacyDirName
+				// '69pmactz.default'
+				&& OS.Path.basename(OS.Path.dirname(dir)).match(/^[0-9a-z]{8}\..+/)
+				// 'Profiles'
+				&& OS.Path.basename(OS.Path.dirname(OS.Path.dirname(dir))) == 'Profiles';
+	},
+	
+	
+	canMigrate: function () {
+		// If (not default location) && (not useDataDir or within legacy location)
+		var currentDir = this.dir;
+		if (currentDir == this.defaultDir) {
+			return false;
+		}
+		
+		// Legacy default or set to legacy default from other program (Standalone/Z4Fx) to share data
+		if (!Zotero.Prefs.get('useDataDir') || this.isLegacy(currentDir)) {
+			return true;
+		}
+		
+		return false;
+	},
+	
+	
+	reveal: function () {
+		return Zotero.File.reveal(this.dir);
+	},
+	
+	
+	markForMigration: function (dir, automatic = false) {
+		return Zotero.File.putContentsAsync(
+			OS.Path.join(dir, this.MIGRATION_MARKER),
+			JSON.stringify({
+				sourceDir: dir,
+				automatic
+			})
+		);
+	},
+	
+	
+	/**
+	 * Migrate data directory if necessary and show any errors
+	 *
+	 * @param {String} dataDir - Current directory
+	 * @param {String} targetDir - Target directory, which may be the same; except in tests, this is
+	 *     the default data directory
+	 */
+	checkForMigration: Zotero.Promise.coroutine(function* (dataDir, newDir) {
+		if (!this.canMigrate(dataDir)) {
+			return false;
+		}
+		
+		let migrationMarker = OS.Path.join(dataDir, this.MIGRATION_MARKER);
+		try {
+			var exists = yield OS.File.exists(migrationMarker)
+		}
+		catch (e) {
+			Zotero.logError(e);
+		}
+		let automatic = false;
+		if (!exists) {
+			// Migrate automatically on macOS and Linux -- this should match the check in
+			// Zotero.File.moveDirectory()
+			if (!Zotero.isWin && (yield OS.File.exists("/bin/mv"))) {
+				automatic = true;
+			}
+			else {
+				return false;
+			}
+		}
+		
+		// Check for an existing pipe from other running versions of Zotero pointing at the same data
+		// directory, and skip migration if found
+		try {
+			let foundPipe = yield Zotero.IPC.pipeExists();
+			if (foundPipe) {
+				Zotero.debug("Found existing pipe -- skipping migration");
+				return false;
+			}
+		}
+		catch (e) {
+			Zotero.logError("Error checking for pipe -- skipping migration:\n\n" + e);
+			return false;
+		}
+		
+		// If there are other profiles pointing to the old directory, make sure we can edit the prefs.js
+		// file before doing anything, or else we risk orphaning a 4.0 installation
+		try {
+			let otherProfiles = yield Zotero.Profile.findOtherProfilesUsingDataDirectory(dataDir);
+			// 'touch' each prefs.js file to make sure we can access it
+			for (let dir of otherProfiles) {
+				let prefs = OS.Path.join(dir, "prefs.js");
+				yield OS.File.setDates(prefs);
+			}
+		}
+		catch (e) {
+			Zotero.logError(e);
+			Zotero.logError("Error checking other profiles -- skipping migration");
+			// TODO: After 5.0 has been out a while, remove this and let migration continue even if
+			// other profile directories can't be altered, with the assumption that they'll be running
+			// 5.0 already and will be pick up the new data directory automatically.
+			return false;
+		}
+		
+		if (automatic) {
+			yield this.markForMigration(dataDir, true);
+		}
+		
+		let sourceDir;
+		let oldDir;
+		let partial = false;
+		
+		// Check whether this is an automatic or manual migration
+		let contents;
+		try {
+			contents = yield Zotero.File.getContentsAsync(migrationMarker);
+			({ sourceDir, automatic } = JSON.parse(contents));
+		}
+		catch (e) {
+			if (contents !== undefined) {
+				Zotero.debug(contents, 1);
+			}
+			Zotero.logError(e);
+			return false;
+		}
+		
+		// Not set to the default directory, so use current as old directory
+		if (dataDir != newDir) {
+			oldDir = dataDir;
+		}
+		// Unfinished migration -- already using new directory, so get path to previous
+		// directory from the migration marker
+		else {
+			oldDir = sourceDir;
+			partial = true;
+		}
+		
+		// Not yet used
+		let progressHandler = function (progress, progressMax) {
+			this.updateZoteroPaneProgressMeter(Math.round(progress / progressMax));
+		}.bind(this);
+		
+		let errors;
+		let mode = automatic ? 'automatic' : 'manual';
+		// This can seemingly fail due to a race condition building the Standalone window,
+		// so just ignore it if it does
+		try {
+			Zotero.showZoteroPaneProgressMeter(Zotero.getString("dataDir.migration.inProgress"));
+		}
+		catch (e) {
+			Zotero.logError(e);
+		}
+		try {
+			errors = yield this.migrate(oldDir, newDir, partial, progressHandler);
+		}
+		catch (e) {
+			// Complete failure (failed to create new directory, copy marker, or move database)
+			Zotero.debug("Migration failed", 1);
+			Zotero.logError(e);
+			
+			let ps = Services.prompt;
+			let buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
+				+ (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_IS_STRING);
+			let index = ps.confirmEx(null,
+				Zotero.getString('dataDir.migration.failure.title'),
+				Zotero.getString(`dataDir.migration.failure.full.${mode}.text1`, ZOTERO_CONFIG.CLIENT_NAME)
+					+ "\n\n"
+					+ e
+					+ "\n\n"
+					+ Zotero.getString(`dataDir.migration.failure.full.${mode}.text2`, Zotero.appName)
+					+ "\n\n"
+					+ Zotero.getString('dataDir.migration.failure.full.current', oldDir)
+					+ "\n\n"
+					+ Zotero.getString('dataDir.migration.failure.full.recommended', newDir),
+				buttonFlags,
+				Zotero.getString('dataDir.migration.failure.full.showCurrentDirectoryAndQuit', Zotero.appName),
+				Zotero.getString('general.notNow'),
+				null, null, {}
+			);
+			if (index == 0) {
+				yield Zotero.File.reveal(oldDir);
+				Zotero.skipLoading = true;
+				Zotero.Utilities.Internal.quitZotero();
+			}
+			return;
+		}
+		
+		// Set data directory again
+		Zotero.debug("Using new data directory " + newDir);
+		this._cache(newDir);
+		// Tell Zotero for Firefox in connector mode to reload and find the new data directory
+		if (Zotero.isStandalone) {
+			Zotero.IPC.broadcast('reinit');
+		}
+		
+		// At least the database was copied, but other things failed
+		if (errors.length) {
+			let ps = Services.prompt;
+			let buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
+				+ (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_IS_STRING)
+				+ (ps.BUTTON_POS_2) * (ps.BUTTON_TITLE_IS_STRING);
+			let index = ps.confirmEx(null,
+				Zotero.getString('dataDir.migration.failure.title'),
+				Zotero.getString(`dataDir.migration.failure.partial.${mode}.text`,
+						[ZOTERO_CONFIG.CLIENT_NAME, Zotero.appName])
+					+ "\n\n"
+					+ Zotero.getString('dataDir.migration.failure.partial.old', oldDir)
+					+ "\n\n"
+					+ Zotero.getString('dataDir.migration.failure.partial.new', newDir),
+				buttonFlags,
+				Zotero.getString('general.tryAgain'),
+				Zotero.getString('general.tryLater'),
+				Zotero.getString('dataDir.migration.failure.partial.showDirectoriesAndQuit', Zotero.appName),
+				null, {}
+			);
+			
+			if (index == 0) {
+				return this.checkForMigration(newDir, newDir);
+			}
+			// Focus the first file/folder in the old directory
+			else if (index == 2) {
+				try {
+					let it = new OS.File.DirectoryIterator(oldDir);
+					let entry;
+					try {
+						entry = yield it.next();
+					}
+					catch (e) {
+						if (e != StopIteration) {
+							throw e;
+						}
+					}
+					finally {
+						it.close();
+					}
+					if (entry) {
+						yield Zotero.File.reveal(entry.path);
+					}
+					// Focus the database file in the new directory
+					yield Zotero.File.reveal(OS.Path.join(newDir, this.getDatabaseFilename()));
+				}
+				catch (e) {
+					Zotero.logError(e);
+				}
+				
+				Zotero.skipLoading = true;
+				Zotero.Utilities.Internal.quitZotero();
+				return;
+			}
+		}
+	}),
+	
+	
+	/**
+	 * Recursively moves data directory from one location to another and updates the data directory
+	 * setting in this profile and any profiles pointing to the old location
+	 *
+	 * If moving the database file fails, an error is thrown.
+	 * Otherwise, an array of errors is returned.
+	 *
+	 * @param {String} oldDir
+	 * @param {String} newDir
+	 * @return {Error[]}
+	 */
+	migrate: Zotero.Promise.coroutine(function* (oldDir, newDir, partial) {
+		var dbName = this.getDatabaseFilename();
+		var errors = [];
+		
+		function addError(e) {
+			errors.push(e);
+			Zotero.logError(e);
+		}
+		
+		if (!(yield OS.File.exists(oldDir))) {
+			Zotero.debug(`Old directory ${oldDir} doesn't exist -- nothing to migrate`);
+			try {
+				let newMigrationMarker = OS.Path.join(newDir, this.MIGRATION_MARKER);
+				Zotero.debug("Removing " + newMigrationMarker);
+				yield OS.File.remove(newMigrationMarker);
+			}
+			catch (e) {
+				Zotero.logError(e);
+			}
+			return [];
+		}
+		
+		if (partial) {
+			Zotero.debug(`Continuing data directory migration from ${oldDir} to ${newDir}`);
+		}
+		else {
+			Zotero.debug(`Migrating data directory from ${oldDir} to ${newDir}`);
+		}
+		
+		// Create the new directory
+		if (!partial) {
+			try {
+				yield OS.File.makeDir(
+					newDir,
+					{
+						ignoreExisting: false,
+						unixMode: 0o755
+					}
+				);
+			}
+			catch (e) {
+				// If default dir exists and is non-empty, move it out of the way
+				// ("Zotero-1", "Zotero-2", …)
+				if (e instanceof OS.File.Error && e.becauseExists) {
+					if (!(yield Zotero.File.directoryIsEmpty(newDir))) {
+						let i = 1;
+						while (true) {
+							let backupDir = newDir + "-" + i++;
+							if (yield OS.File.exists(backupDir)) {
+								if (i > 5) {
+									throw new Error("Too many backup directories "
+										+ "-- stopped at " + backupDir);
+								}
+								continue;
+							}
+							Zotero.debug(`Moving existing directory to ${backupDir}`);
+							yield Zotero.File.moveDirectory(newDir, backupDir);
+							break;
+						}
+						yield OS.File.makeDir(
+							newDir,
+							{
+								ignoreExisting: false,
+								unixMode: 0o755
+							}
+						);
+					}
+				}
+				else {
+					throw e;
+				}
+			}
+		}
+		
+		// Copy marker
+		let oldMarkerFile = OS.Path.join(oldDir, this.MIGRATION_MARKER);
+		// Marker won't exist on subsequent attempts after partial failure
+		if (yield OS.File.exists(oldMarkerFile)) {
+			yield OS.File.copy(oldMarkerFile, OS.Path.join(newDir, this.MIGRATION_MARKER));
+		}
+		
+		// Update the data directory setting first. If moving the database fails, get() will continue
+		// to use the old directory based on the migration marker
+		this.set(newDir);
+		
+		// Move database
+		if (!partial) {
+			Zotero.debug("Moving " + dbName);
+			yield OS.File.move(OS.Path.join(oldDir, dbName), OS.Path.join(newDir, dbName));
+		}
+		
+		// Once the database has been moved, we can clear the migration marker from the old directory.
+		// If the migration is interrupted after this, it can be continued later based on the migration
+		// marker in the new directory.
+		try {
+			yield OS.File.remove(OS.Path.join(oldDir, this.MIGRATION_MARKER));
+		}
+		catch (e) {
+			addError(e);
+		}
+		
+		errors = errors.concat(yield Zotero.File.moveDirectory(
+			oldDir,
+			newDir,
+			{
+				allowExistingTarget: true,
+				// Don't overwrite root files (except for hidden files like .DS_Store)
+				noOverwrite: path => {
+					return OS.Path.dirname(path) == oldDir && !OS.Path.basename(path).startsWith('.')
+				},
+			}
+		));
+		
+		if (errors.length) {
+			Zotero.logError("Not all files were transferred from " + oldDir + " to " + newDir);
+		}
+		else {
+			try {
+				let newMigrationMarker = OS.Path.join(newDir, this.MIGRATION_MARKER);
+				Zotero.debug("Removing " + newMigrationMarker);
+				yield OS.File.remove(newMigrationMarker);
+				
+				Zotero.debug("Migration successful");
+			}
+			catch (e) {
+				addError(e);
+			}
+		}
+		
+		// Update setting in other profiles that point to this data directory
+		try {
+			let otherProfiles = yield Zotero.Profile.findOtherProfilesUsingDataDirectory(oldDir);
+			for (let dir of otherProfiles) {
+				try {
+					yield Zotero.Profile.updateProfileDataDirectory(dir, oldDir, newDir);
+				}
+				catch (e) {
+					Zotero.logError("Error updating " + OS.Path.join(dir.path, "prefs.js"));
+					Zotero.logError(e);
+				}
+			}
+		}
+		catch (e) {
+			Zotero.logError("Error updating other profiles to point to new location");
+		}
+		
+		return errors;
+	}),
+	
+	
+	getDatabaseFilename: function (name) {
+		return (name || ZOTERO_CONFIG.ID) + '.sqlite';
+	},
+	
+	getDatabase: function (name, ext) {
+		name = this.getDatabaseFilename(name);
+		ext = ext ? '.' + ext : '';
+		
+		return OS.Path.join(this.dir, name + ext);
+	}
+};
diff --git a/chrome/content/zotero/xpcom/file.js b/chrome/content/zotero/xpcom/file.js
index 876c8bfc0d..969d57ace3 100644
--- a/chrome/content/zotero/xpcom/file.js
+++ b/chrome/content/zotero/xpcom/file.js
@@ -444,7 +444,6 @@ Zotero.File = new function(){
 		var it = new OS.File.DirectoryIterator(path);
 		try {
 			let entry = yield it.next();
-			Zotero.debug(entry);
 			return false;
 		}
 		catch (e) {
diff --git a/chrome/content/zotero/xpcom/profile.js b/chrome/content/zotero/xpcom/profile.js
new file mode 100644
index 0000000000..713bffbc76
--- /dev/null
+++ b/chrome/content/zotero/xpcom/profile.js
@@ -0,0 +1,236 @@
+/*
+    ***** BEGIN LICENSE BLOCK *****
+    
+    Copyright © 2016 Center for History and New Media
+                     George Mason University, Fairfax, Virginia, USA
+                     http://zotero.org
+    
+    This file is part of Zotero.
+    
+    Zotero is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+    
+    Zotero is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+    
+    You should have received a copy of the GNU Affero General Public License
+    along with Zotero.  If not, see <http://www.gnu.org/licenses/>.
+    
+    ***** END LICENSE BLOCK *****
+*/
+
+"use strict";
+
+Components.utils.import("resource://gre/modules/osfile.jsm");
+
+Zotero.Profile = {
+	dir: OS.Constants.Path.profileDir,
+	
+	getDefaultInProfilesDir: Zotero.Promise.coroutine(function* (profilesDir) {
+		var profilesIni = OS.Path.join(profilesDir, "profiles.ini");
+		
+		try {
+			var iniContents = yield Zotero.File.getContentsAsync(profilesIni);
+		}
+		catch (e) {
+			if (e instanceof OS.File.Error && e.becauseNoSuchFile) {
+				return false;
+			}
+			throw e;
+		}
+		
+		// cheap and dirty ini parser
+		var curSection = null;
+		var defaultSection = null;
+		var nSections = 0;
+		for (let line of iniContents.split(/(?:\r?\n|\r)/)) {
+			let tline = line.trim();
+			if(tline[0] == "[" && tline[tline.length-1] == "]") {
+				curSection = {};
+				if(tline != "[General]") nSections++;
+			} else if(curSection && tline != "") {
+				let equalsIndex = tline.indexOf("=");
+				let key = tline.substr(0, equalsIndex);
+				let val = tline.substr(equalsIndex+1);
+				curSection[key] = val;
+				if(key == "Default" && val == "1") {
+					defaultSection = curSection;
+				}
+			}
+		}
+		if (!defaultSection && curSection) defaultSection = curSection;
+		
+		if (!defaultSection || !defaultSection.Path) return false;
+		
+		var defaultProfile = defaultSection.IsRelative === "1"
+			? OS.Path.join(profilesDir, ...defaultSection.Path.split("/"))
+			: defaultSection.Path;
+		
+		if (!(yield OS.File.exists(defaultProfile))) {
+			return false;
+		}
+		return [defaultProfile, nSections > 1];
+	}),
+	
+	
+	getProfilesDir: function () {
+		return OS.Path.dirname(this.dir);
+	},
+	
+	
+	/**
+	 * Get the path to the Profiles directory of the other app from this one (Firefox or Zotero),
+	 * which may or may not exist
+	 *
+	 * @return {String} - Path
+	 */
+	getOtherAppProfilesDir: function () {
+		var dir = OS.Path.dirname(OS.Path.dirname(OS.Path.dirname(this.dir)));
+		
+		if (Zotero.isStandalone) {
+			if (Zotero.isWin) {
+				dir = OS.Path.join(OS.Path.dirname(dir), "Mozilla", "Firefox");
+			}
+			else if (Zotero.isMac) {
+				dir = OS.Path.join(dir, "Firefox");
+			}
+			else {
+				dir = OS.Path.join(dir, ".mozilla", "firefox");
+			}
+		}
+		else {
+			if (Zotero.isWin) {
+				dir = OS.Path.join(OS.Path.dirname(dir), "Zotero", "Zotero");
+			}
+			else if (Zotero.isMac) {
+				dir = OS.Path.join(dir, "Zotero");
+			} else {
+				dir = OS.Path.join(dir, ".zotero", "zotero");
+			}
+		}
+		
+		return OS.Path.join(dir, "Profiles");
+	},
+	
+	
+	/**
+	 * Find other profile directories (for this app or the other app) using the given data directory
+	 *
+	 * @return {String[]}
+	 */
+	findOtherProfilesUsingDataDirectory: Zotero.Promise.coroutine(function* (dataDir) {
+		let otherAppProfiles = yield this._findOtherAppProfiles();
+		let otherProfiles = (yield this._findOtherProfiles()).concat(otherAppProfiles);
+		
+		// First get profiles pointing at this directory
+		otherProfiles = yield Zotero.Promise.filter(otherProfiles, Zotero.Promise.coroutine(function* (dir) {
+			let prefs = yield Zotero.File.getContentsAsync(OS.Path.join(dir, "prefs.js"));
+			prefs = prefs.trim().split(/(?:\r\n|\r|\n)/);
+			
+			return prefs.some(line => {
+				return line.includes("extensions.zotero.useDataDir") && line.includes("true");
+			}) && prefs.some(line => {
+				return line.match(/extensions\.zotero\.(lastD|d)ataDir/) && line.includes(dataDir)
+			});
+		}));
+		
+		// If the parent of the source directory is a profile directory from the other app, add that
+		// to the list, which addresses the situation where the source directory is a custom
+		// location for the current profile but is a default in the other app (meaning it wouldn't
+		// be added above).
+		let dataDirParent = OS.Path.dirname(dataDir);
+		if (otherAppProfiles.includes(dataDirParent) && !otherProfiles.includes(dataDirParent)) {
+			otherProfiles.push(dataDirParent);
+		}
+		
+		if (otherProfiles.length) {
+			Zotero.debug("Found other profiles pointing to " + dataDir);
+			Zotero.debug(otherProfiles);
+		}
+		else {
+			Zotero.debug("No other profiles point to " + dataDir);
+		}
+		
+		return otherProfiles;
+	}),
+	
+	
+	updateProfileDataDirectory: Zotero.Promise.coroutine(function* (profileDir, oldDir, newDir) {
+		let prefsFile = OS.Path.join(profileDir, "prefs.js");
+		let prefsFileTmp = OS.Path.join(profileDir, "prefs.js.tmp");
+		Zotero.debug("Updating " + prefsFile + " to point to new data directory");
+		let contents = yield Zotero.File.getContentsAsync(prefsFile);
+		contents = contents
+			.trim()
+			.split(/(?:\r\n|\r|\n)/)
+			// Remove existing lines
+			.filter(line => !line.match(/extensions\.zotero\.(useD|lastD|d)ataDir/));
+		// Shouldn't happen, but let's make sure we don't corrupt the prefs file
+		let safeVal = newDir.replace(/["]/g, "");
+		contents.push(
+			`user_pref("extensions.zotero.dataDir", "${safeVal}");`,
+			`user_pref("extensions.zotero.lastDataDir", "${safeVal}");`,
+			'user_pref("extensions.zotero.useDataDir", true);'
+		);
+		let lineSep = Zotero.isWin ? "\r\n" : "\n";
+		contents = contents.join(lineSep) + lineSep;
+		yield OS.File.writeAtomic(
+			prefsFile,
+			contents,
+			{
+				tmpPath: prefsFileTmp,
+				encoding: 'utf-8'
+			}
+		);
+	}),
+	
+	
+	//
+	// Private methods
+	//
+	
+	/**
+	 * Get all profile directories within the given directory
+	 *
+	 * @return {String[]} - Array of paths
+	 */
+	_getProfilesInDir: Zotero.Promise.coroutine(function* (profilesDir) {
+		var dirs = [];
+		yield Zotero.File.iterateDirectory(profilesDir, function* (iterator) {
+			while (true) {
+				let entry = yield iterator.next();
+				if (entry.isDir && (yield OS.File.exists(OS.Path.join(entry.path, "prefs.js")))) {
+					dirs.push(entry.path);
+				}
+			}
+		});
+		return dirs;
+	}),
+	
+	
+	/**
+	 * Find other profile directories for this app (Firefox or Zotero)
+	 *
+	 * @return {String[]} - Array of paths
+	 */
+	_findOtherProfiles: Zotero.Promise.coroutine(function* () {
+		var profileDir = this.dir;
+		var profilesDir = this.getProfilesDir();
+		return this._getProfilesInDir(profilesDir).filter(dir => dir != profileDir);
+	}),
+	
+	
+	/**
+	 * Find profile directories for the other app (Firefox or Zotero)
+	 *
+	 * @return {String[]} - Array of paths
+	 */
+	_findOtherAppProfiles: Zotero.Promise.coroutine(function* () {
+		var dir = this.getOtherAppProfilesDir();
+		return (yield OS.File.exists(dir)) ? this._getProfilesInDir(dir) : [];
+	})
+};
diff --git a/chrome/content/zotero/xpcom/sync/syncLocal.js b/chrome/content/zotero/xpcom/sync/syncLocal.js
index 2987fad352..2dace66dae 100644
--- a/chrome/content/zotero/xpcom/sync/syncLocal.js
+++ b/chrome/content/zotero/xpcom/sync/syncLocal.js
@@ -138,7 +138,7 @@ Zotero.Sync.Data.Local = {
 				accept = true;
 			}
 			// else if (io.extra1) {
-			// 	if (Zotero.forceNewDataDirectory(win)) {
+			// 	if (Zotero.DataDirectory.forceChange(win)) {
 			// 		var ps = Services.prompt;
 			// 		ps.alert(null,
 			// 			Zotero.getString('general.restartRequired'),
diff --git a/chrome/content/zotero/xpcom/zotero.js b/chrome/content/zotero/xpcom/zotero.js
index 7572ca9128..143ee040ed 100644
--- a/chrome/content/zotero/xpcom/zotero.js
+++ b/chrome/content/zotero/xpcom/zotero.js
@@ -34,9 +34,7 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
  */
  (function(){
 	// Privileged (public) methods
-	this.getProfileDirectory = getProfileDirectory;
 	this.getStorageDirectory = getStorageDirectory;
-	this.chooseZoteroDirectory = chooseZoteroDirectory;
 	this.debug = debug;
 	this.log = log;
 	this.logError = logError;
@@ -103,7 +101,6 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 	this.hiDPISuffix = "";
 	
 	var _startupErrorHandler;
-	var _dataDirectory = false;
 	var _localizedStringBundle;
 	
 	var _locked = false;
@@ -275,7 +272,8 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 		_addToolbarIcon();
 		
 		try {
-			var dataDir = Zotero.getZoteroDirectory();
+			yield Zotero.DataDirectory.init();
+			var dataDir = Zotero.DataDirectory.dir;
 		}
 		catch (e) {
 			// Zotero dir not found
@@ -301,11 +299,11 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 					
 					// Revert to home directory
 					if (index == 1) {
-						Zotero.chooseZoteroDirectory(false, true);
+						Zotero.DataDirectory.choose(false, true);
 					}
 					// Locate data directory
 					else if (index == 2) {
-						Zotero.chooseZoteroDirectory();
+						Zotero.DataDirectory.choose();
 					}
 				}
 				_addToolbarIcon();
@@ -318,14 +316,16 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 		}
 		
 		if (!Zotero.isConnector) {
-			yield Zotero.checkForDataDirectoryMigration(dataDir.path, this.getDefaultDataDir());
+			yield Zotero.DataDirectory.checkForMigration(
+				dataDir, Zotero.DataDirectory.defaultDir
+			);
 			if (this.skipLoading) {
 				return;
 			}
 			
 			// Make sure data directory isn't in Dropbox, etc.
 			if (Zotero.isStandalone) {
-				Zotero.checkForUnsafeDataDirectory(dataDir.path);
+				yield Zotero.DataDirectory.checkForUnsafeLocation(dataDir);
 			}
 		}
 		
@@ -456,9 +456,9 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 		Zotero.VersionHeader.init();
 		
 		// Check for data reset/restore
-		var dataDir = Zotero.getZoteroDirectory();
-		var restoreFile = OS.Path.join(dataDir.path, 'restore-from-server');
-		var resetDataDirFile = OS.Path.join(dataDir.path, 'reset-data-directory');
+		var dataDir = Zotero.DataDirectory.dir;
+		var restoreFile = OS.Path.join(dataDir, 'restore-from-server');
+		var resetDataDirFile = OS.Path.join(dataDir, 'reset-data-directory');
 		
 		var result = yield Zotero.Promise.all([OS.File.exists(restoreFile), OS.File.exists(resetDataDirFile)]);
 		if (result.some(r => r)) {
@@ -478,7 +478,7 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 					Zotero.restoreFromServer = true;
 				} else if (Zotero.resetDataDir) {
 					Zotero.initAutoSync = true;
-					var storageDir = OS.Path.join(dataDir.path, 'storage');
+					var storageDir = OS.Path.join(dataDir, 'storage');
 					yield Zotero.Promise.all([
 						OS.File.removeDir(storageDir, {ignoreAbsent: true}), 
 						OS.File.remove(resetDataDirFile)
@@ -509,9 +509,6 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 			if (Zotero.isStandalone) {
 				let dbSystemVersion = yield Zotero.Schema.getDBVersion('system');
 				if (dbSystemVersion > 0 && dbSystemVersion < 31) {
-					var dir = Zotero.getProfileDirectory();
-					dir.append('zotero');
-		
 					var ps = Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
 								.createInstance(Components.interfaces.nsIPromptService);
 					var buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
@@ -534,8 +531,6 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 					
 					// Default location
 					if (index == 0) {
-						Zotero.File.createDirectoryIfMissing(dir);
-						
 						Zotero.Prefs.set("useDataDir", false)
 						
 						Services.startup.quit(
@@ -545,7 +540,7 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 					}
 					// Select new data directory
 					else if (index == 1) {
-						var dir = Zotero.chooseZoteroDirectory(true);
+						let dir = yield Zotero.DataDirectory.choose(true);
 						if (!dir) {
 							quit = true;
 						}
@@ -889,284 +884,18 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 	});
 	
 	
-	function getProfileDirectory(){
-		return Services.dirsvc.get("ProfD", Components.interfaces.nsIFile);
-	}
-	
-	function getDefaultProfile(prefDir) {
-		// find profiles.ini file
-		var profilesIni = prefDir.clone();
-		profilesIni.append("profiles.ini");
-		if(!profilesIni.exists()) return false;
-		var iniContents = Zotero.File.getContents(profilesIni);
-		
-		// cheap and dirty ini parser
-		var curSection = null;
-		var defaultSection = null;
-		var nSections = 0;
-		for (let line of iniContents.split(/(?:\r?\n|\r)/)) {
-			let tline = line.trim();
-			if(tline[0] == "[" && tline[tline.length-1] == "]") {
-				curSection = {};
-				if(tline != "[General]") nSections++;
-			} else if(curSection && tline != "") {
-				let equalsIndex = tline.indexOf("=");
-				let key = tline.substr(0, equalsIndex);
-				let val = tline.substr(equalsIndex+1);
-				curSection[key] = val;
-				if(key == "Default" && val == "1") {
-					defaultSection = curSection;
-				}
-			}
-		}
-		if(!defaultSection && curSection) defaultSection = curSection;
-		
-		// parse out ini to reveal profile
-		if(!defaultSection || !defaultSection.Path) return false;
-		
-		
-		if(defaultSection.IsRelative === "1") {
-			var defaultProfile = prefDir.clone().QueryInterface(Components.interfaces.nsILocalFile);
-			try {
-				for each(var dir in defaultSection.Path.split("/")) defaultProfile.append(dir);
-			} catch(e) {
-				Zotero.logError("Could not find profile at "+defaultSection.Path);
-				throw e;
-			}
-		} else {
-			var defaultProfile = Components.classes["@mozilla.org/file/local;1"]
-				.createInstance(Components.interfaces.nsILocalFile);
-			defaultProfile.initWithPath(defaultSection.Path);
-		}
-		
-		if(!defaultProfile.exists()) return false;
-		return [defaultProfile, nSections > 1];
+	this.getProfileDirectory = function () {
+		Zotero.warn("Zotero.getProfileDirectory() is deprecated -- use Zotero.Profile.dir");
+		return Zotero.File.pathToFile(Zotero.Profile.dir);
 	}
 	
 	
 	this.getZoteroDirectory = function () {
-		if (_dataDirectory != false) {
-			return Zotero.File.pathToFile(_dataDirectory);
-		}
-		
-		var file;
-		if (Zotero.Prefs.get('useDataDir')) {
-			file = Components.classes["@mozilla.org/file/local;1"]
-				.createInstance(Components.interfaces.nsILocalFile);
-			
-			let prefVal = Zotero.Prefs.get('dataDir');
-			// Convert old persistent descriptor pref to string path and clear obsolete lastDataDir pref
-			//
-			// persistentDescriptor now appears to return (and parse) a string path anyway on macOS,
-			// which is the only place where it didn't use a string path to begin with, but be explicit
-			// just in case there's some difference.
-			//
-			// A post-Mozilla prefs migration should do this same check, and then this conditional can
-			// be removed.
-			if (Zotero.Prefs.get('lastDataDir')) {
-				try {
-					file.persistentDescriptor = prefVal;
-				}
-				catch (e) {
-					Zotero.debug("Persistent descriptor in extensions.zotero.dataDir did not resolve", 1);
-					e = { name: "NS_ERROR_FILE_NOT_FOUND" };
-					throw (e);
-				}
-				// This removes lastDataDir
-				this.setDataDirectory(file.path);
-			}
-			else {
-				// If there's a migration marker in this directory and no database, migration was
-				// interrupted before the database could be moved (or moving failed), so use the source
-				// directory specified in the marker file.
-				let migrationMarker = OS.Path.join(prefVal, this.DATA_DIR_MIGRATION_MARKER);
-				let dbFile = OS.Path.join(prefVal, this.getDatabaseFilename());
-				if (Zotero.File.pathToFile(migrationMarker).exists()
-						&& !(Zotero.File.pathToFile(dbFile).exists())) {
-					let contents = Zotero.File.getContents(migrationMarker);
-					try {
-						let { sourceDir } = JSON.parse(contents);
-						file = Zotero.File.pathToFile(sourceDir);
-					}
-					catch (e) {
-						Zotero.logError(e);
-						Zotero.debug(`Invalid marker file:\n\n${contents}`, 1);
-						e = { name: "NS_ERROR_FILE_NOT_FOUND" };
-						throw e;
-					}
-				}
-				else {
-					try {
-						file = Zotero.File.pathToFile(prefVal);
-					}
-					catch (e) {
-						Zotero.logError(e);
-						Zotero.debug(`Invalid path '${prefVal}' in dataDir pref`, 1);
-						e = { name: "NS_ERROR_FILE_NOT_FOUND" };
-						throw e;
-					}
-				}
-			}
-			
-			if (!file.exists() && file.path != this.getDefaultDataDir()) {
-				// If set to a legacy directory that doesn't exist, forget about it and just use the
-				// new default location, which will either exist or be created below. The most likely
-				// cause of this is a migration, so don't bother looking in other-app profiles.
-				if (this.isLegacyDataDirectory(file.path)) {
-					let newDefault = this.getDefaultDataDir();
-					Zotero.debug(`Legacy data directory ${file.path} from pref not found `
-						+ `-- reverting to ${newDefault}`, 1);
-					file = Zotero.File.pathToFile(newDefault);
-					this.setDataDirectory(newDefault);
-				}
-				// For other custom directories that don't exist, show not-found dialog
-				else {
-					Zotero.debug("Custom data directory ${file.path} not found", 1);
-					throw { name: "NS_ERROR_FILE_NOT_FOUND" };
-				}
-			}
-		}
-		else {
-			let dataDir = this.getDefaultDataDir();
-			
-			//
-			// TODO: asyncify
-			//
-			
-			// Check for ~/Zotero/zotero.sqlite
-			dataDir = Zotero.File.pathToFile(dataDir);
-			let dbFile = dataDir.clone();
-			dbFile.append(this.getDatabaseFilename());
-			if (dbFile.exists()) {
-				Zotero.debug("Using data directory " + dataDir.path);
-				this._cacheDataDirectory(dataDir.path);
-				
-				// Set as a custom data directory so that 4.0 uses it
-				this.setDataDirectory(dataDir.path);
-				
-				return dataDir.clone();
-			}
-			
-			// Check for 'zotero' dir in profile dir
-			let profileSubdir = Zotero.getProfileDirectory();
-			profileSubdir.append('zotero');
-			if (profileSubdir.exists()) {
-				Zotero.debug("Using data directory " + profileSubdir.path);
-				this._cacheDataDirectory(profileSubdir.path);
-				return profileSubdir.clone();
-			}
-			
-			//
-			// If Standalone and no directory yet, check Firefox directory, or vice versa
-			//
-			let prefDir = OS.Path.dirname(
-				OS.Path.dirname(
-					OS.Path.dirname(
-						OS.Constants.Path.profileDir
-					)
-				)
-			);
-			
-			if(Zotero.isStandalone) {
-				if (Zotero.isWin) {
-					prefDir = OS.Path.join(OS.Path.dirname(prefDir), "Mozilla", "Firefox");
-				}
-				else if (Zotero.isMac) {
-					prefDir = OS.Path.join(prefDir, "Firefox");
-				}
-				else {
-					prefDir = OS.Path.join(prefDir, ".mozilla", "firefox");
-				}
-			}
-			else {
-				if (Zotero.isWin) {
-					prefDir = OS.Path.join(OS.Path.dirname(prefDir), "Zotero", "Zotero");
-				}
-				else if (Zotero.isMac) {
-					prefDir = OS.Path.join(prefDir, "Zotero");
-				} else {
-					prefDir = OS.Path.join(prefDir, ".zotero", "zotero");
-				}
-			}
-			
-			Zotero.debug("Looking for existing profile in " + prefDir);
-			
-			// get default profile
-			var defProfile;
-			try {
-				defProfile = getDefaultProfile(Zotero.File.pathToFile(prefDir));
-			} catch(e) {
-				Zotero.debug("An error occurred locating the Firefox profile; not "+
-					"attempting to migrate from Zotero for Firefox");
-				Zotero.logError(e);
-			}
-			
-			if(defProfile) {
-				// get Zotero directory
-				let profileDir = defProfile[0].path;
-				Zotero.debug("Found default profile at " + profileDir);
-				
-				// copy prefs
-				let prefsFile = OS.Path.join(profileDir, "prefs.js");
-				if (Zotero.File.pathToFile(prefsFile).exists()) {
-					// build sandbox
-					var sandbox = new Components.utils.Sandbox("http://www.example.com/");
-					Components.utils.evalInSandbox(
-						"var prefs = {};"+
-						"function user_pref(key, val) {"+
-							"prefs[key] = val;"+
-						"}"
-					, sandbox);
-					
-					// remove comments
-					var prefsJs = Zotero.File.getContents(prefsFile);
-					prefsJs = prefsJs.replace(/^#[^\r\n]*$/mg, "");
-					
-					// evaluate
-					Components.utils.evalInSandbox(prefsJs, sandbox);
-					var prefs = sandbox.prefs;
-					for(var key in prefs) {
-						if(key.substr(0, ZOTERO_CONFIG.PREF_BRANCH.length) === ZOTERO_CONFIG.PREF_BRANCH
-								&& key !== "extensions.zotero.firstRun2") {
-							Zotero.Prefs.set(key.substr(ZOTERO_CONFIG.PREF_BRANCH.length), prefs[key]);
-						}
-					}
-					
-					// If data directory setting was transferred, use that
-					if (Zotero.Prefs.get('useDataDir')) {
-						return this.getZoteroDirectory();
-					}
-				}
-				
-				// If there's a data directory in the default profile for the alternative app, use that
-				let zoteroDir = OS.Path.join(profileDir, ZOTERO_CONFIG.ID);
-				if (Zotero.File.pathToFile(zoteroDir).exists()) {
-					this.setDataDirectory(zoteroDir);
-					file = Zotero.File.pathToFile(zoteroDir);
-				}
-			}
-			
-			if (!file) {
-				file = dataDir;
-			}
-		}
-		
-		Zotero.debug("Using data directory " + file.path);
-		Zotero.File.createDirectoryIfMissing(file);
-		this._cacheDataDirectory(file.path);
-		return file.clone();
+		Zotero.warn("Zotero.getZoteroDirectory() is deprecated -- use Zotero.DataDirectory.dir");
+		return Zotero.File.pathToFile(Zotero.DataDirectory.dir);
 	}
 	
 	
-	this.getDefaultDataDir = function () {
-		// Use special data directory for tests
-		if (Zotero.test) {
-			return OS.Path.join(OS.Path.dirname(OS.Constants.Path.profileDir), "Zotero");
-		}
-		return OS.Path.join(OS.Constants.Path.homeDir, ZOTERO_CONFIG.CLIENT_NAME);
-	};
-	
-	
 	function getStorageDirectory(){
 		var file = Zotero.getZoteroDirectory();
 		
@@ -1176,17 +905,9 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 	}
 	
 	
-	this.getDatabaseFilename = function (name) {
-		return (name || ZOTERO_CONFIG.ID) + '.sqlite';
-	};
-	
 	this.getZoteroDatabase = function (name, ext) {
-		name = this.getDatabaseFilename(name);
-		ext = ext ? '.' + ext : '';
-		
-		var file = Zotero.getZoteroDirectory();
-		file.append(name + ext);
-		return file;
+		Zotero.warn("Zotero.getZoteroDatabase() is deprecated -- use Zotero.DataDirectory.getDatabase()");
+		return Zotero.File.pathToFile(Zotero.DataDirectory.getDatabase(name, ext));
 	}
 	
 	
@@ -1229,582 +950,6 @@ Components.utils.import("resource://gre/modules/osfile.jsm");
 	}
 	
 	
-	function chooseZoteroDirectory(forceQuitNow, useHomeDir, moreInfoCallback) {
-		var win = Services.wm.getMostRecentWindow('navigator:browser');
-		var ps = Services.prompt;
-		
-		if (useHomeDir) {
-			let changed = this.setDataDirectory(this.getDefaultDataDir());
-			if (!changed) {
-				return false;
-			}
-		}
-		else {
-			var nsIFilePicker = Components.interfaces.nsIFilePicker;
-			while (true) {
-				var fp = Components.classes["@mozilla.org/filepicker;1"]
-							.createInstance(nsIFilePicker);
-				fp.init(win, Zotero.getString('dataDir.selectDir'), nsIFilePicker.modeGetFolder);
-				fp.displayDirectory = Zotero.getZoteroDirectory();
-				fp.appendFilters(nsIFilePicker.filterAll);
-				if (fp.show() == nsIFilePicker.returnOK) {
-					var file = fp.file;
-					let dialogText = '';
-					let dialogTitle = '';
-					
-					if (file.path == (Zotero.Prefs.get('lastDataDir') || Zotero.Prefs.get('dataDir'))) {
-						Zotero.debug("Data directory hasn't changed");
-						return false;
-					}
-					
-					// In dropbox folder
-					if (Zotero.File.isDropboxDirectory(file.path)) {
-						dialogTitle = Zotero.getString('general.warning');
-						dialogText = Zotero.getString('dataDir.unsafeLocation.selected.dropbox') + "\n\n"
-								+ Zotero.getString('dataDir.unsafeLocation.selected.useAnyway');
-					}
-					else if (file.directoryEntries.hasMoreElements()) {
-						let dbfile = file.clone();
-						dbfile.append(this.getDatabaseFilename());
-						
-						// Warn if non-empty and no zotero.sqlite
-						if (!dbfile.exists()) {
-							dialogTitle = Zotero.getString('dataDir.selectedDirNonEmpty.title');
-							dialogText = Zotero.getString('dataDir.selectedDirNonEmpty.text');
-						}
-					}
-					// Directory empty
-					else {
-						dialogTitle = Zotero.getString('dataDir.selectedDirEmpty.title');
-						dialogText = Zotero.getString('dataDir.selectedDirEmpty.text', Zotero.appName) + '\n\n'
-								+ Zotero.getString('dataDir.selectedDirEmpty.useNewDir');
-					}
-					// Warning dialog to be displayed
-					if(dialogText !== '') {
-						let buttonFlags = ps.STD_YES_NO_BUTTONS;
-						if (moreInfoCallback) {
-							buttonFlags += ps.BUTTON_POS_2 * ps.BUTTON_TITLE_IS_STRING;
-						}
-						let index = ps.confirmEx(null,
-							dialogTitle,
-							dialogText,
-							buttonFlags,
-							null,
-							null,
-							moreInfoCallback ? Zotero.getString('general.moreInformation') : null,
-							null, {});
-
-						// Not OK -- return to file picker
-						if (index == 1) {
-							continue;
-						}
-						else if (index == 2) {
-							setTimeout(function () {
-								moreInfoCallback();
-							}, 1);
-							return false;
-						}
-					}
-
-					this.setDataDirectory(file.path);
-					
-					break;
-				}
-				else {
-					return false;
-				}
-			}
-		}
-		
-		var buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING);
-		if (!forceQuitNow) {
-			buttonFlags += (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_IS_STRING);
-		}
-		var app = Zotero.appName;
-		var index = ps.confirmEx(null,
-			Zotero.getString('general.restartRequired'),
-			Zotero.getString('general.restartRequiredForChange', app)
-				+ "\n\n" + Zotero.getString('dataDir.moveFilesToNewLocation', app),
-			buttonFlags,
-			Zotero.getString('general.quitApp', app),
-			forceQuitNow ? null : Zotero.getString('general.restartLater'),
-			null, null, {});
-		
-		if (forceQuitNow || index == 0) {
-			Services.startup.quit(Components.interfaces.nsIAppStartup.eAttemptQuit);
-		}
-		
-		return useHomeDir ? true : file;
-	}
-	
-	
-	this._cacheDataDirectory = function (dir) {
-		_dataDirectory = dir;
-	};
-	
-	
-	this.forceNewDataDirectory = function(win) {
-		if (!win) {
-			win = Services.wm.getMostRecentWindow('navigator:browser');
-		}
-		var ps = Services.prompt;
-		
-		var nsIFilePicker = Components.interfaces.nsIFilePicker;
-		while (true) {
-			var fp = Components.classes["@mozilla.org/filepicker;1"]
-						.createInstance(nsIFilePicker);
-			fp.init(win, Zotero.getString('dataDir.selectNewDir', Zotero.clientName), nsIFilePicker.modeGetFolder);
-			fp.displayDirectory = Zotero.getZoteroDirectory();
-			fp.appendFilters(nsIFilePicker.filterAll);
-			if (fp.show() == nsIFilePicker.returnOK) {
-				var file = fp.file;
-				
-				if (file.directoryEntries.hasMoreElements()) {
-					ps.alert(null,
-						Zotero.getString('dataDir.mustSelectEmpty.title'),
-						Zotero.getString('dataDir.mustSelectEmpty.text')
-					);
-					continue;
-				}
-				
-				this.setDataDirectory(file.path);
-				
-				return file;
-			} else {
-				return false;
-			}
-		}
-	};
-
-
-	this.warnOnUnsafeDataDir = true;
-	this.checkForUnsafeDataDirectory = function (path) {
-		if (this.warnOnUnsafeDataDir && Zotero.File.isDropboxDirectory(path)
-				&& Zotero.Prefs.get('warnOnUnsafeDataDir')) {
-			
-			this.warnOnUnsafeDataDir = false;
-			let check = {value: false};
-			let index = Services.prompt.confirmEx(
-				null,
-				Zotero.getString('general.warning'),
-				Zotero.getString('dataDir.unsafeLocation.existing.dropbox') + "\n\n"
-					+ Zotero.getString('dataDir.unsafeLocation.existing.chooseDifferent'),
-				Services.prompt.STD_YES_NO_BUTTONS,
-				null, null, null,
-				Zotero.getString('general.dontShowWarningAgain'),
-				check
-			);
-
-			// Yes - display dialog.
-			if (index == 0) {
-				Zotero.chooseZoteroDirectory(true);
-			}
-			if (check.value) {
-				Zotero.Prefs.set('warnOnUnsafeDataDir', false);
-			}
-		}
-	}
-	
-	
-	/**
-	 * @return {Boolean} - True if the directory changed; false otherwise
-	 */
-	this.setDataDirectory = function (path) {
-		var origPath = Zotero.Prefs.get('dataDir');
-		
-		Zotero.Prefs.set('dataDir', path);
-		// Clear legacy pref
-		Zotero.Prefs.clear('lastDataDir');
-		Zotero.Prefs.set('useDataDir', true);
-		
-		return path != origPath;
-	};
-	
-	
-	this.isLegacyDataDirectory = function (dir) {
-		// 'zotero'
-		return OS.Path.basename(dir) == ZOTERO_CONFIG.ID
-				// '69pmactz.default'
-				&& OS.Path.basename(OS.Path.dirname(dir)).match(/^[0-9a-z]{8}\..+/)
-				// 'Profiles'
-				&& OS.Path.basename(OS.Path.dirname(OS.Path.dirname(dir))) == 'Profiles';
-	}
-	
-	
-	this.canMigrateDataDirectory = function () {
-		// If (not default location) && (not useDataDir or within legacy location)
-		var currentDir = this.getZoteroDirectory().path;
-		if (currentDir == this.getDefaultDataDir()) {
-			return false;
-		}
-		
-		// Legacy default or set to legacy default from other program (Standalone/Z4Fx) to share data
-		if (!Zotero.Prefs.get('useDataDir') || this.isLegacyDataDirectory(currentDir)) {
-			return true;
-		}
-		
-		return false;
-	};
-	
-	
-	this.revealDataDirectory = function () {
-		return Zotero.File.reveal(this.getZoteroDirectory().path);
-	},
-	
-	
-	this.DATA_DIR_MIGRATION_MARKER = 'migrate-dir';
-	
-	
-	this.markDataDirectoryForMigration = function (dir, automatic = false) {
-		return Zotero.File.putContentsAsync(
-			OS.Path.join(dir, this.DATA_DIR_MIGRATION_MARKER),
-			JSON.stringify({
-				sourceDir: dir,
-				automatic
-			})
-		);
-	};
-	
-	
-	/**
-	 * Migrate data directory if necessary and show any errors
-	 *
-	 * @param {String} dataDir - Current directory
-	 * @param {String} targetDir - Target directory, which may be the same; except in tests, this is
-	 *     the default data directory
-	 */
-	this.checkForDataDirectoryMigration = Zotero.Promise.coroutine(function* (dataDir, newDir) {
-		if (!this.canMigrateDataDirectory(dataDir)) {
-			return false;
-		}
-		
-		let migrationMarker = OS.Path.join(dataDir, this.DATA_DIR_MIGRATION_MARKER);
-		try {
-			var exists = yield OS.File.exists(migrationMarker)
-		}
-		catch (e) {
-			Zotero.logError(e);
-		}
-		let automatic = false;
-		if (!exists) {
-			// Migrate automatically on macOS and Linux -- this should match the check in
-			// Zotero.File.moveDirectory()
-			if (!Zotero.isWin && (yield OS.File.exists("/bin/mv"))) {
-				automatic = true;
-			}
-			else {
-				return false;
-			}
-		}
-		
-		// Check for an existing pipe from other running versions of Zotero pointing at the same data
-		// directory, and skip migration if found
-		try {
-			let foundPipe = yield Zotero.IPC.pipeExists();
-			if (foundPipe) {
-				Zotero.debug("Found existing pipe -- skipping migration");
-				return false;
-			}
-		}
-		catch (e) {
-			Zotero.logError("Error checking for pipe -- skipping migration:\n\n" + e);
-			return false;
-		}
-		
-		if (automatic) {
-			yield this.markDataDirectoryForMigration(dataDir, true);
-		}
-		
-		let sourceDir;
-		let oldDir;
-		let partial = false;
-		
-		// Check whether this is an automatic or manual migration
-		let contents;
-		try {
-			contents = yield Zotero.File.getContentsAsync(migrationMarker);
-			({ sourceDir, automatic } = JSON.parse(contents));
-		}
-		catch (e) {
-			if (contents !== undefined) {
-				Zotero.debug(contents, 1);
-			}
-			Zotero.logError(e);
-			return false;
-		}
-		
-		// Not set to the default directory, so use current as old directory
-		if (dataDir != newDir) {
-			oldDir = dataDir;
-		}
-		// Unfinished migration -- already using new directory, so get path to previous
-		// directory from the migration marker
-		else {
-			oldDir = sourceDir;
-			partial = true;
-		}
-		
-		// Not yet used
-		let progressHandler = function (progress, progressMax) {
-			this.updateZoteroPaneProgressMeter(Math.round(progress / progressMax));
-		}.bind(this);
-		
-		let errors;
-		let mode = automatic ? 'automatic' : 'manual';
-		// This can seemingly fail due to a race condition building the Standalone window,
-		// so just ignore it if it does
-		try {
-			this.showZoteroPaneProgressMeter(Zotero.getString("dataDir.migration.inProgress"));
-		}
-		catch (e) {
-			Zotero.logError(e);
-		}
-		try {
-			errors = yield Zotero.migrateDataDirectory(oldDir, newDir, partial, progressHandler);
-		}
-		catch (e) {
-			// Complete failure (failed to create new directory, copy marker, or move database)
-			Zotero.debug("Migration failed", 1);
-			Zotero.logError(e);
-			
-			let ps = Services.prompt;
-			let buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
-				+ (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_IS_STRING);
-			let index = ps.confirmEx(null,
-				Zotero.getString('dataDir.migration.failure.title'),
-				Zotero.getString(`dataDir.migration.failure.full.${mode}.text1`, ZOTERO_CONFIG.CLIENT_NAME)
-					+ "\n\n"
-					+ e
-					+ "\n\n"
-					+ Zotero.getString(`dataDir.migration.failure.full.${mode}.text2`, Zotero.appName)
-					+ "\n\n"
-					+ Zotero.getString('dataDir.migration.failure.full.current', oldDir)
-					+ "\n\n"
-					+ Zotero.getString('dataDir.migration.failure.full.recommended', newDir),
-				buttonFlags,
-				Zotero.getString('dataDir.migration.failure.full.showCurrentDirectoryAndQuit', Zotero.appName),
-				Zotero.getString('general.notNow'),
-				null, null, {}
-			);
-			if (index == 0) {
-				yield Zotero.File.reveal(oldDir);
-				this.skipLoading = true;
-				Zotero.Utilities.Internal.quitZotero();
-			}
-			return;
-		}
-		
-		// Set data directory again
-		Zotero.debug("Using new data directory " + newDir);
-		this._cacheDataDirectory(newDir);
-		// Tell Zotero for Firefox in connector mode to reload and find the new data directory
-		if (this.isStandalone) {
-			Zotero.IPC.broadcast('reinit');
-		}
-		
-		// At least the database was copied, but other things failed
-		if (errors.length) {
-			let ps = Services.prompt;
-			let buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
-				+ (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_IS_STRING)
-				+ (ps.BUTTON_POS_2) * (ps.BUTTON_TITLE_IS_STRING);
-			let index = ps.confirmEx(null,
-				Zotero.getString('dataDir.migration.failure.title'),
-				Zotero.getString(`dataDir.migration.failure.partial.${mode}.text`,
-						[ZOTERO_CONFIG.CLIENT_NAME, Zotero.appName])
-					+ "\n\n"
-					+ Zotero.getString('dataDir.migration.failure.partial.old', oldDir)
-					+ "\n\n"
-					+ Zotero.getString('dataDir.migration.failure.partial.new', newDir),
-				buttonFlags,
-				Zotero.getString('general.tryAgain'),
-				Zotero.getString('general.tryLater'),
-				Zotero.getString('dataDir.migration.failure.partial.showDirectoriesAndQuit', Zotero.appName),
-				null, {}
-			);
-			
-			if (index == 0) {
-				return this.checkForDataDirectoryMigration(newDir, newDir);
-			}
-			// Focus the first file/folder in the old directory
-			else if (index == 2) {
-				try {
-					let it = new OS.File.DirectoryIterator(oldDir);
-					let entry;
-					try {
-						entry = yield it.next();
-					}
-					catch (e) {
-						if (e != StopIteration) {
-							throw e;
-						}
-					}
-					finally {
-						it.close();
-					}
-					if (entry) {
-						yield Zotero.File.reveal(entry.path);
-					}
-					// Focus the database file in the new directory
-					yield Zotero.File.reveal(OS.Path.join(newDir, this.getDatabaseFilename()));
-				}
-				catch (e) {
-					Zotero.logError(e);
-				}
-				
-				Zotero.skipLoading = true;
-				Zotero.Utilities.Internal.quitZotero();
-				return;
-			}
-		}
-	});
-	
-	
-	/**
-	 * Recursively moves data directory from one location to another
-	 * and updates the data directory setting
-	 *
-	 * If moving the database file fails, an error is thrown.
-	 * Otherwise, an array of errors is returned.
-	 *
-	 * @param {String} oldDir
-	 * @param {String} newDir
-	 * @return {Error[]}
-	 */
-	this.migrateDataDirectory = Zotero.Promise.coroutine(function* (oldDir, newDir, partial) {
-		var dbName = this.getDatabaseFilename();
-		var errors = [];
-		
-		function addError(e) {
-			errors.push(e);
-			Zotero.logError(e);
-		}
-		
-		if (!(yield OS.File.exists(oldDir))) {
-			Zotero.debug(`Old directory ${oldDir} doesn't exist -- nothing to migrate`);
-			try {
-				let newMigrationMarker = OS.Path.join(newDir, Zotero.DATA_DIR_MIGRATION_MARKER);
-				Zotero.debug("Removing " + newMigrationMarker);
-				yield OS.File.remove(newMigrationMarker);
-			}
-			catch (e) {
-				Zotero.logError(e);
-			}
-			return [];
-		}
-		
-		if (partial) {
-			Zotero.debug(`Continuing data directory migration from ${oldDir} to ${newDir}`);
-		}
-		else {
-			Zotero.debug(`Migrating data directory from ${oldDir} to ${newDir}`);
-		}
-		
-		// Create the new directory
-		if (!partial) {
-			try {
-				yield OS.File.makeDir(
-					newDir,
-					{
-						ignoreExisting: false,
-						unixMode: 0o755
-					}
-				);
-			}
-			catch (e) {
-				// If default dir exists and is non-empty, move it out of the way
-				// ("Zotero-1", "Zotero-2", …)
-				if (e instanceof OS.File.Error && e.becauseExists) {
-					if (!(yield Zotero.File.directoryIsEmpty(newDir))) {
-						let i = 1;
-						while (true) {
-							let backupDir = newDir + "-" + i++;
-							if (yield OS.File.exists(backupDir)) {
-								if (i > 5) {
-									throw new Error("Too many backup directories "
-										+ "-- stopped at " + backupDir);
-								}
-								continue;
-							}
-							Zotero.debug(`Moving existing directory to ${backupDir}`);
-							yield Zotero.File.moveDirectory(newDir, backupDir);
-							break;
-						}
-						yield OS.File.makeDir(
-							newDir,
-							{
-								ignoreExisting: false,
-								unixMode: 0o755
-							}
-						);
-					}
-				}
-				else {
-					throw e;
-				}
-			}
-		}
-		
-		// Copy marker
-		let oldMarkerFile = OS.Path.join(oldDir, this.DATA_DIR_MIGRATION_MARKER);
-		// Marker won't exist on subsequent attempts after partial failure
-		if (yield OS.File.exists(oldMarkerFile)) {
-			yield OS.File.copy(oldMarkerFile, OS.Path.join(newDir, this.DATA_DIR_MIGRATION_MARKER));
-		}
-		
-		// Update the data directory setting first. If moving the database fails, getZoteroDirectory()
-		// will continue to use the old directory based on the migration marker
-		Zotero.setDataDirectory(newDir);
-		
-		// Move database
-		if (!partial) {
-			Zotero.debug("Moving " + dbName);
-			yield OS.File.move(OS.Path.join(oldDir, dbName), OS.Path.join(newDir, dbName));
-		}
-		
-		// Once the database has been moved, we can clear the migration marker from the old directory.
-		// If the migration is interrupted after this, it can be continued later based on the migration
-		// marker in the new directory.
-		try {
-			yield OS.File.remove(OS.Path.join(oldDir, this.DATA_DIR_MIGRATION_MARKER));
-		}
-		catch (e) {
-			addError(e);
-		}
-		
-		errors = errors.concat(yield Zotero.File.moveDirectory(
-			oldDir,
-			newDir,
-			{
-				allowExistingTarget: true,
-				// Don't overwrite root files (except for hidden files like .DS_Store)
-				noOverwrite: path => {
-					return OS.Path.dirname(path) == oldDir && !OS.Path.basename(path).startsWith('.')
-				},
-			}
-		));
-		
-		if (errors.length) {
-			Zotero.logError("Not all files were transferred from " + oldDir + " to " + newDir);
-		}
-		else {
-			try {
-				let newMigrationMarker = OS.Path.join(newDir, Zotero.DATA_DIR_MIGRATION_MARKER);
-				Zotero.debug("Removing " + newMigrationMarker);
-				yield OS.File.remove(newMigrationMarker);
-				
-				Zotero.debug("Migration successful");
-			}
-			catch (e) {
-				addError(e);
-			}
-		}
-		
-		return errors;
-	});
-	
-	
-	
 	/**
 	 * Launch a file, the best way we can
 	 */
diff --git a/components/zotero-service.js b/components/zotero-service.js
index b4560eb307..97d3ec301c 100644
--- a/components/zotero-service.js
+++ b/components/zotero-service.js
@@ -33,6 +33,7 @@ const Ci = Components.interfaces;
 /** XPCOM files to be loaded for all modes **/
 const xpcomFilesAll = [
 	'zotero',
+	'dataDirectory',
 	'date',
 	'debug',
 	'error',
@@ -41,6 +42,7 @@ const xpcomFilesAll = [
 	'mimeTypeHandler',
 	'openurl',
 	'ipc',
+	'profile',
 	'progressWindow',
 	'translation/translate',
 	'translation/translate_firefox',
diff --git a/test/content/support.js b/test/content/support.js
index 1a629e13e4..ce2a75ddd0 100644
--- a/test/content/support.js
+++ b/test/content/support.js
@@ -474,7 +474,6 @@ function getTestDataUrl(path) {
 
 /**
  * Returns an absolute path to an empty temporary directory
- * (i.e., test/tests/data)
  */
 var getTempDirectory = Zotero.Promise.coroutine(function* getTempDirectory() {
 	Components.utils.import("resource://gre/modules/osfile.jsm");
diff --git a/test/tests/zoteroTest.js b/test/tests/dataDirectoryTest.js
similarity index 89%
rename from test/tests/zoteroTest.js
rename to test/tests/dataDirectoryTest.js
index 75912fc5f7..cb10023c5f 100644
--- a/test/tests/zoteroTest.js
+++ b/test/tests/dataDirectoryTest.js
@@ -1,6 +1,6 @@
 "use strict";
 
-describe("Zotero Core Functions", function () {
+describe("Zotero.DataDirectory", function () {
 	var tmpDir, oldDir, newDir, dbFilename, oldDBFile, newDBFile, oldStorageDir, newStorageDir,
 		oldTranslatorsDir, newTranslatorsDir, translatorName1, translatorName2,
 		oldStorageDir1, newStorageDir1, storageFile1, oldStorageDir2, newStorageDir2, storageFile2,
@@ -12,7 +12,7 @@ describe("Zotero Core Functions", function () {
 		tmpDir = yield getTempDirectory();
 		oldDir = OS.Path.join(tmpDir, "old");
 		newDir = OS.Path.join(tmpDir, "new");
-		dbFilename = Zotero.getDatabaseFilename();
+		dbFilename = Zotero.DataDirectory.getDatabaseFilename();
 		oldDBFile = OS.Path.join(oldDir, dbFilename);
 		newDBFile = OS.Path.join(newDir, dbFilename);
 		oldStorageDir = OS.Path.join(oldDir, "storage");
@@ -33,24 +33,23 @@ describe("Zotero Core Functions", function () {
 		str4 = '4';
 		str5 = '5';
 		str6 = '6';
-		oldMigrationMarker = OS.Path.join(oldDir, Zotero.DATA_DIR_MIGRATION_MARKER);
-		newMigrationMarker = OS.Path.join(newDir, Zotero.DATA_DIR_MIGRATION_MARKER);
+		oldMigrationMarker = OS.Path.join(oldDir, Zotero.DataDirectory.MIGRATION_MARKER);
+		newMigrationMarker = OS.Path.join(newDir, Zotero.DataDirectory.MIGRATION_MARKER);
 		
-		stubs.canMigrate = sinon.stub(Zotero, "canMigrateDataDirectory").returns(true);
+		stubs.canMigrate = sinon.stub(Zotero.DataDirectory, "canMigrate").returns(true);
 		// A pipe always exists during tests, since Zotero is running
 		stubs.pipeExists = sinon.stub(Zotero.IPC, "pipeExists").returns(Zotero.Promise.resolve(false));
 	});
 	
 	beforeEach(function* () {
-		// Trigger a call to setDataDirectory() now to avoid affecting the stub call count
-		Zotero.getZoteroDirectory();
-		stubs.setDataDir = sinon.stub(Zotero, "setDataDirectory");
+		stubs.setDataDir = sinon.stub(Zotero.DataDirectory, "set");
 	});
 	
 	afterEach(function* () {
 		yield removeDir(oldDir);
 		yield removeDir(newDir);
-		Zotero._cacheDataDirectory(false);
+		Zotero.DataDirectory._cache(false);
+		yield Zotero.DataDirectory.init();
 		
 		stubs.setDataDir.restore();
 	});
@@ -83,7 +82,7 @@ describe("Zotero Core Functions", function () {
 		let storageDir1 = OS.Path.join(storageDir, 'AAAAAAAA');
 		let storageDir2 = OS.Path.join(storageDir, 'BBBBBBBB');
 		let translatorsDir = OS.Path.join(dir, 'translators');
-		let migrationMarker = OS.Path.join(dir, Zotero.DATA_DIR_MIGRATION_MARKER);
+		let migrationMarker = OS.Path.join(dir, Zotero.DataDirectory.MIGRATION_MARKER);
 		
 		// Database
 		yield Zotero.File.putContentsAsync(OS.Path.join(dir, dbFilename), str1);
@@ -141,7 +140,7 @@ describe("Zotero Core Functions", function () {
 	});
 	
 	
-	describe("#checkForDataDirectoryMigration()", function () {
+	describe("#checkForMigration()", function () {
 		let fileMoveStub;
 		
 		before(function () {
@@ -198,7 +197,7 @@ describe("Zotero Core Functions", function () {
 						)
 					);
 				});
-				yield Zotero.checkForDataDirectoryMigration(oldDir, newDir);
+				yield Zotero.DataDirectory.checkForMigration(oldDir, newDir);
 				yield promise;
 				yield promise2;
 				
@@ -240,7 +239,7 @@ describe("Zotero Core Functions", function () {
 						)
 					);
 				});
-				yield Zotero.checkForDataDirectoryMigration(oldDir, newDir);
+				yield Zotero.DataDirectory.checkForMigration(oldDir, newDir);
 				yield promise;
 				
 				assert.isTrue(stub2.calledOnce);
@@ -267,7 +266,7 @@ describe("Zotero Core Functions", function () {
 		
 		it("should remove marker if old directory doesn't exist", function* () {
 			yield populateDataDirectory(newDir, oldDir);
-			yield Zotero.checkForDataDirectoryMigration(newDir, newDir);
+			yield Zotero.DataDirectory.checkForMigration(newDir, newDir);
 			yield checkMigration({
 				skipSetDataDirectory: true
 			});
@@ -275,7 +274,7 @@ describe("Zotero Core Functions", function () {
 	});
 	
 	
-	describe("#migrateDataDirectory()", function () {
+	describe("#migrate()", function () {
 		// Define tests and store for running in non-mv mode
 		var tests = [];
 		function add(desc, fn) {
@@ -285,7 +284,7 @@ describe("Zotero Core Functions", function () {
 		
 		add("should move all files and folders", function* () {
 			yield populateDataDirectory(oldDir);
-			yield Zotero.migrateDataDirectory(oldDir, newDir);
+			yield Zotero.DataDirectory.migrate(oldDir, newDir);
 			yield checkMigration();
 		});
 		
@@ -295,7 +294,7 @@ describe("Zotero Core Functions", function () {
 			
 			yield OS.File.copy(oldMigrationMarker, newMigrationMarker);
 			
-			yield Zotero.migrateDataDirectory(oldDir, newDir, true);
+			yield Zotero.DataDirectory.migrate(oldDir, newDir, true);
 			yield checkMigration();
 		});
 		
@@ -306,7 +305,7 @@ describe("Zotero Core Functions", function () {
 			yield OS.File.copy(oldMigrationMarker, newMigrationMarker);
 			yield OS.File.move(OS.Path.join(oldDir, dbFilename), OS.Path.join(newDir, dbFilename));
 			
-			yield Zotero.migrateDataDirectory(oldDir, newDir, true);
+			yield Zotero.DataDirectory.migrate(oldDir, newDir, true);
 			yield checkMigration();
 		});
 		
@@ -322,7 +321,7 @@ describe("Zotero Core Functions", function () {
 			yield removeDir(newTranslatorsDir);
 			yield removeDir(newStorageDir2);
 			
-			yield Zotero.migrateDataDirectory(oldDir, newDir, true);
+			yield Zotero.DataDirectory.migrate(oldDir, newDir, true);
 			yield checkMigration();
 		});
 		
@@ -331,7 +330,7 @@ describe("Zotero Core Functions", function () {
 			yield OS.File.makeDir(newDir, { unixMode: 0o755 });
 			yield Zotero.File.putContentsAsync(OS.Path.join(newDir, 'existing'), '');
 			
-			yield Zotero.migrateDataDirectory(oldDir, newDir);
+			yield Zotero.DataDirectory.migrate(oldDir, newDir);
 			yield checkMigration();
 			
 			assert.isTrue(yield OS.File.exists(OS.Path.join(newDir + "-1", 'existing')));
@@ -374,7 +373,7 @@ describe("Zotero Core Functions", function () {
 					}
 				});
 				
-				yield Zotero.migrateDataDirectory(oldDir, newDir);
+				yield Zotero.DataDirectory.migrate(oldDir, newDir);
 				
 				stub1.restore();
 				
diff --git a/test/tests/profileTest.js b/test/tests/profileTest.js
new file mode 100644
index 0000000000..64762049cb
--- /dev/null
+++ b/test/tests/profileTest.js
@@ -0,0 +1,190 @@
+"use strict";
+
+describe("Zotero.Profile", function () {
+	var tmpDir;
+	var profile1 = "ht79g2qb.Test1";
+	var profile2 = "b9auumgf.Test2";
+	var profile3 = "7sgqhns3.Test3";
+	
+	beforeEach(function* () {
+		tmpDir = yield getTempDirectory();
+		var contents = `[General]
+StartWithLastProfile=0
+
+[Profile0]
+Name=Test 1
+IsRelative=1
+Path=Profiles/${profile1}
+Default=1
+
+[Profile1]
+Name=Test 2
+IsRelative=1
+Path=Profiles/${profile2}
+
+[Profile1]
+Name=Test 3
+IsRelative=1
+Path=Profiles/${profile3}
+`;
+		yield Zotero.File.putContentsAsync(OS.Path.join(tmpDir, "profiles.ini"), contents);
+		yield OS.File.makeDir(
+			OS.Path.join(tmpDir, "Profiles", profile1),
+			{
+				unixMode: 0o755,
+				from: tmpDir
+			}
+		);
+		yield OS.File.makeDir(OS.Path.join(tmpDir, "Profiles", profile2), { unixMode: 0o755 });
+		yield OS.File.makeDir(OS.Path.join(tmpDir, "Profiles", profile3), { unixMode: 0o755 });
+	});
+	
+	
+	describe("#getDefaultInProfilesDir()", function () {
+		it("should parse a profiles.ini file", function* () {
+			var [dir, multiple] = yield Zotero.Profile.getDefaultInProfilesDir(tmpDir);
+			assert.equal(dir, OS.Path.join(tmpDir, "Profiles", profile1));
+		});
+	});
+	
+	
+	describe("#findOtherProfilesUsingDataDirectory()", function () {
+		it("should find profile with directory as a custom location", function* () {
+			let dataDir = Zotero.DataDirectory.dir;
+			let contents1 = `user_pref("extensions.lastAppVersion", "49.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+`;
+			let contents2 = `user_pref("extensions.lastAppVersion", "50.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.zotero.dataDir", "${dataDir}");
+user_pref("extensions.zotero.useDataDir", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+`;
+			let otherDir = OS.Path.join(OS.Path.dirname(dataDir), "Other");
+			let contents3 = `user_pref("extensions.lastAppVersion", "51.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.zotero.dataDir", "${otherDir}");
+user_pref("extensions.zotero.useDataDir", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+`;
+			
+			let prefsFile1 = OS.Path.join(tmpDir, "Profiles", profile1, "prefs.js");
+			let prefsFile2 = OS.Path.join(tmpDir, "Profiles", profile2, "prefs.js");
+			let prefsFile3 = OS.Path.join(tmpDir, "Profiles", profile3, "prefs.js");
+			yield Zotero.File.putContentsAsync(prefsFile1, contents1);
+			yield Zotero.File.putContentsAsync(prefsFile2, contents2);
+			yield Zotero.File.putContentsAsync(prefsFile3, contents3);
+			
+			var stub = sinon.stub(Zotero.Profile, "getOtherAppProfilesDir")
+				.returns(OS.Path.join(tmpDir, "Profiles"));
+			
+			var dirs = yield Zotero.Profile.findOtherProfilesUsingDataDirectory(dataDir);
+			
+			stub.restore();
+			
+			assert.sameMembers(dirs, [OS.Path.join(tmpDir, "Profiles", profile2)]);
+			assert.lengthOf(dirs, 1);
+		});
+		
+		
+		it("should find other-app profile with directory as a legacy default location", function* () {
+			let contents1 = `user_pref("extensions.lastAppVersion", "49.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+`;
+			let contents2 = `user_pref("extensions.lastAppVersion", "50.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+`;
+			
+			let prefsFile1 = OS.Path.join(tmpDir, "Profiles", profile1, "prefs.js");
+			let prefsFile2 = OS.Path.join(tmpDir, "Profiles", profile2, "prefs.js");
+			yield Zotero.File.putContentsAsync(prefsFile1, contents1);
+			yield Zotero.File.putContentsAsync(prefsFile2, contents2);
+			
+			var stub = sinon.stub(Zotero.Profile, "getOtherAppProfilesDir")
+				.returns(OS.Path.join(tmpDir, "Profiles"));
+			
+			Components.utils.import("resource://zotero/config.js");
+			var dirs = yield Zotero.Profile.findOtherProfilesUsingDataDirectory(
+				OS.Path.join(OS.Path.dirname(prefsFile1), Zotero.DataDirectory.legacyDirName)
+			);
+			
+			stub.restore();
+			
+			assert.sameMembers(dirs, [OS.Path.join(tmpDir, "Profiles", profile1)]);
+			assert.lengthOf(dirs, 1);
+		});
+	});
+	
+	
+	describe("#updateProfileDataDirectory()", function () {
+		it("should add new lines to prefs.js", function* () {
+			let prefsFile = OS.Path.join(tmpDir, "Profiles", profile1, "prefs.js");
+			let oldDir = OS.Path.join(OS.Path.dirname(tmpDir), "Old", "Zotero");
+			let newDir = OS.Path.join(OS.Path.dirname(tmpDir), "New", "Zotero");
+			
+			let contents = `user_pref("extensions.lastAppVersion", "50.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+`;
+			let addition = `user_pref("extensions.zotero.dataDir", "${newDir}");
+user_pref("extensions.zotero.lastDataDir", "${newDir}");
+user_pref("extensions.zotero.useDataDir", true);
+`;
+			
+			yield Zotero.File.putContentsAsync(prefsFile, contents);
+			yield Zotero.Profile.updateProfileDataDirectory(
+				OS.Path.join(tmpDir, "Profiles", profile1),
+				oldDir,
+				newDir
+			);
+			
+			let newContents = yield Zotero.File.getContentsAsync(prefsFile);
+			
+			assert.equal(newContents, contents + addition);
+		});
+		
+		
+		it("should replace existing lines in prefs.js", function* () {
+			let prefsFile = OS.Path.join(tmpDir, "Profiles", profile1, "prefs.js");
+			let oldDir = OS.Path.join(OS.Path.dirname(tmpDir), "Old", "Zotero");
+			let newDir = OS.Path.join(OS.Path.dirname(tmpDir), "New", "Zotero");
+			
+			let contents = `user_pref("extensions.lastAppVersion", "50.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.zotero.dataDir", "old-mac-persistent-descriptor");
+user_pref("extensions.zotero.lastDataDir", "${oldDir}");
+user_pref("extensions.zotero.useDataDir", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+`;
+			let expectedContents = `user_pref("extensions.lastAppVersion", "50.0");
+user_pref("extensions.shownSelectionUI", true);
+user_pref("extensions.ui.locale.hidden", true);
+user_pref("loop.copy.ticket", 196);
+user_pref("extensions.zotero.dataDir", "${newDir}");
+user_pref("extensions.zotero.lastDataDir", "${newDir}");
+user_pref("extensions.zotero.useDataDir", true);
+`;
+			
+			yield Zotero.File.putContentsAsync(prefsFile, contents);
+			yield Zotero.Profile.updateProfileDataDirectory(
+				OS.Path.join(tmpDir, "Profiles", profile1),
+				oldDir,
+				newDir
+			);
+			
+			let newContents = yield Zotero.File.getContentsAsync(prefsFile);
+			
+			assert.equal(newContents, expectedContents);
+		});
+	});
+});
diff --git a/test/tests/syncLocalTest.js b/test/tests/syncLocalTest.js
index 02202655e6..e2e9aa91e3 100644
--- a/test/tests/syncLocalTest.js
+++ b/test/tests/syncLocalTest.js
@@ -79,7 +79,7 @@ describe("Zotero.Sync.Data.Local", function() {
 		
 		// extra1 functionality not used at the moment
 		it.skip("should prompt for data reset and allow to choose a new data directory", function* (){
-			sinon.stub(Zotero, 'forceNewDataDirectory').returns(true);
+			sinon.stub(Zotero.DataDirectory, 'forceChange').returns(true);
 			yield Zotero.Users.setCurrentUserID(1);
 			yield Zotero.Users.setCurrentUsername("A");
 			
@@ -88,10 +88,10 @@ describe("Zotero.Sync.Data.Local", function() {
 			var cont = yield Zotero.Sync.Data.Local.checkUser(window, 2, "B");
 			var resetDataDirFileExists = yield OS.File.exists(resetDataDirFile);
 			assert.isTrue(cont);
-			assert.isTrue(Zotero.forceNewDataDirectory.called);
+			assert.isTrue(Zotero.DataDirectory.forceChange.called);
 			assert.isFalse(resetDataDirFileExists);
 			
-			Zotero.forceNewDataDirectory.restore();
+			Zotero.DataDirectory.forceChange.restore();
 		});
 	});