diff --git a/chrome/content/zotero/errorReport.xul b/chrome/content/zotero/errorReport.xul
index 868edb5b3f..b0042802cb 100644
--- a/chrome/content/zotero/errorReport.xul
+++ b/chrome/content/zotero/errorReport.xul
@@ -53,8 +53,13 @@
 						body += key + '=' + encodeURIComponent(parts[key]) + '&';
 					}
 					body = body.substr(0, body.length - 1);
-					Zotero.HTTP.doPost("https://repo.zotero.org/repo/report", body,
-						_sendErrorReportCallback);
+					var url = 'https://repo.zotero.org/repo/report';
+					Zotero.HTTP.promise('POST', url,
+						{ body: body, successCodes: false, foreground: true })
+					.then(function (xmlhttp) {
+						_sendErrorReportCallback(xmlhttp);
+					})
+					.done();
 				});
 			}
 			
diff --git a/chrome/content/zotero/preferences/preferences_sync.js b/chrome/content/zotero/preferences/preferences_sync.js
index 8b4263e734..4b3af6a883 100644
--- a/chrome/content/zotero/preferences/preferences_sync.js
+++ b/chrome/content/zotero/preferences/preferences_sync.js
@@ -333,7 +333,11 @@ Zotero_Preferences.Sync = {
 						
 						// TODO: better way of checking for an active session?
 						if (Zotero.Sync.Server.sessionIDComponent == 'sessionid=') {
-							Zotero.Sync.Server.login(callback);
+							Zotero.Sync.Server.login()
+							.then(function () {
+								callback();
+							})
+							.done();
 						}
 						else {
 							callback();
diff --git a/chrome/content/zotero/xpcom/http.js b/chrome/content/zotero/xpcom/http.js
index fd52a66ecf..fec534de72 100644
--- a/chrome/content/zotero/xpcom/http.js
+++ b/chrome/content/zotero/xpcom/http.js
@@ -53,11 +53,12 @@ Zotero.HTTP = new function() {
 	 *         <li>cookieSandbox - The sandbox from which cookies should be taken</li>
 	 *         <li>debug - Log response text and status code</li>
 	 *         <li>dontCache - If set, specifies that the request should not be fulfilled from the cache</li>
+	 *         <li>foreground - Make a foreground request, showing certificate/authentication dialogs if necessary</li>
 	 *         <li>headers - HTTP headers to include in the request</li>
 	 *         <li>requestObserver - Callback to receive XMLHttpRequest after open()</li>
 	 *         <li>responseType - The type of the response. See XHR 2 documentation for legal values</li>
 	 *         <li>responseCharset - The charset the response should be interpreted as</li>
-	 *         <li>successCodes - HTTP status codes that are considered successful</li>
+	 *         <li>successCodes - HTTP status codes that are considered successful, or FALSE to allow all</li>
 	 *     </ul>
 	 * @param {Zotero.CookieSandbox} [cookieSandbox] Cookie sandbox object
 	 * @return {Promise} A promise resolved with the XMLHttpRequest object if the request
@@ -105,7 +106,9 @@ Zotero.HTTP = new function() {
 		var xmlhttp = Components.classes["@mozilla.org/xmlextras/xmlhttprequest;1"]
 					.createInstance();
 		// Prevent certificate/authentication dialogs from popping up
-		xmlhttp.mozBackgroundRequest = true;
+		if (!options || !options.foreground) {
+			xmlhttp.mozBackgroundRequest = true;
+		}
 		xmlhttp.open(method, url, true);
 		
 		// Pass the request to a callback
@@ -157,6 +160,10 @@ Zotero.HTTP = new function() {
 			if (options && options.successCodes) {
 				var success = options.successCodes.indexOf(status) != -1;
 			}
+			// Explicit FALSE means allow any status code
+			else if (options && options.successCodes === false) {
+				var success = true;
+			}
 			else if(isFile) {
 				var success = status == 200 || status == 0;
 			}
diff --git a/chrome/content/zotero/xpcom/sync.js b/chrome/content/zotero/xpcom/sync.js
index 52b9b3eadf..d4d9df50f4 100644
--- a/chrome/content/zotero/xpcom/sync.js
+++ b/chrome/content/zotero/xpcom/sync.js
@@ -1345,7 +1345,7 @@ Zotero.Sync.Server = new function () {
 		}
 	};
 	
-	function login(callback) {
+	function login() {
 		var url = _serverURL + "login";
 		
 		var username = Zotero.Sync.Server.username;
@@ -1368,7 +1368,9 @@ Zotero.Sync.Server = new function () {
 		
 		Zotero.Sync.Runner.setSyncStatus(Zotero.getString('sync.status.loggingIn'));
 		
-		Zotero.HTTP.doPost(url, body, function (xmlhttp) {
+		return Zotero.HTTP.promise("POST", url,
+			{ body: body, successCodes: false, foreground: !Zotero.Sync.Runner.background })
+		.then(function (xmlhttp) {
 			_checkResponse(xmlhttp, true);
 			
 			var response = xmlhttp.responseXML.childNodes[0];
@@ -1396,10 +1398,6 @@ Zotero.Sync.Server = new function () {
 			
 			
 			//Zotero.debug('Got session ID ' + _sessionID + ' from server');
-			
-			if (callback) {
-				callback();
-			}
 		});
 	}
 	
@@ -1416,9 +1414,11 @@ Zotero.Sync.Server = new function () {
 		
 		if (!_sessionID) {
 			Zotero.debug("Session ID not available -- logging in");
-			Zotero.Sync.Server.login(function () {
+			Zotero.Sync.Server.login()
+			.then(function () {
 				Zotero.Sync.Server.sync(_callbacks);
-			});
+			})
+			.done();
 			return;
 		}
 		
@@ -1472,9 +1472,11 @@ Zotero.Sync.Server = new function () {
 				Zotero.debug("Invalid session ID -- logging in");
 				_sessionID = false;
 				_syncInProgress = false;
-				Zotero.Sync.Server.login(function () {
+				Zotero.Sync.Server.login()
+				.then(function () {
 					Zotero.Sync.Server.sync(_callbacks);
-				});
+				})
+				.done();
 				return;
 			}
 			
@@ -1800,9 +1802,11 @@ Zotero.Sync.Server = new function () {
 	function clear(callback) {
 		if (!_sessionID) {
 			Zotero.debug("Session ID not available -- logging in");
-			Zotero.Sync.Server.login(function () {
+			Zotero.Sync.Server.login()
+			.then(function () {
 				Zotero.Sync.Server.clear(callback);
-			});
+			})
+			.done();
 			return;
 		}
 		
@@ -1814,9 +1818,11 @@ Zotero.Sync.Server = new function () {
 			if (_invalidSession(xmlhttp)) {
 				Zotero.debug("Invalid session ID -- logging in");
 				_sessionID = false;
-				Zotero.Sync.Server.login(function () {
+				Zotero.Sync.Server.login()
+				.then(function () {
 					Zotero.Sync.Server.clear(callback);
-				});
+				})
+				.done();
 				return;
 			}
 			
@@ -1896,27 +1902,29 @@ Zotero.Sync.Server = new function () {
 		if (!xmlhttp.responseText) {
 			var channel = xmlhttp.channel;
 			// Check SSL cert
-			var secInfo = channel.securityInfo;
-			if (secInfo instanceof Ci.nsITransportSecurityInfo) {
-				secInfo.QueryInterface(Ci.nsITransportSecurityInfo);
-				if ((secInfo.securityState & Ci.nsIWebProgressListener.STATE_IS_INSECURE) == Ci.nsIWebProgressListener.STATE_IS_INSECURE) {
-					var url = channel.name;
-					var ios = Components.classes["@mozilla.org/network/io-service;1"].
-								getService(Components.interfaces.nsIIOService);
-					try {
-						var uri = ios.newURI(url, null, null);
-						var host = uri.host;
+			if (channel) {
+				var secInfo = channel.securityInfo;
+				if (secInfo instanceof Ci.nsITransportSecurityInfo) {
+					secInfo.QueryInterface(Ci.nsITransportSecurityInfo);
+					if ((secInfo.securityState & Ci.nsIWebProgressListener.STATE_IS_INSECURE) == Ci.nsIWebProgressListener.STATE_IS_INSECURE) {
+						var url = channel.name;
+						var ios = Components.classes["@mozilla.org/network/io-service;1"].
+									getService(Components.interfaces.nsIIOService);
+						try {
+							var uri = ios.newURI(url, null, null);
+							var host = uri.host;
+						}
+						catch (e) {
+							Zotero.debug(e);
+						}
+						var kbURL = 'http://zotero.org/support/kb/ssl_certificate_error';
+						_error(Zotero.getString('sync.storage.error.webdav.sslCertificateError', host) + "\n\n"
+							+ Zotero.getString('general.seeForMoreInformation', kbURL),
+							false, noReloadOnFailure);
 					}
-					catch (e) {
-						Zotero.debug(e);
+					else if ((secInfo.securityState & Ci.nsIWebProgressListener.STATE_IS_BROKEN) == Ci.nsIWebProgressListener.STATE_IS_BROKEN) {
+						_error(Zotero.getString('sync.error.sslConnectionError'), false, noReloadOnFailure);
 					}
-					var kbURL = 'http://zotero.org/support/kb/ssl_certificate_error';
-					_error(Zotero.getString('sync.storage.error.webdav.sslCertificateError', host) + "\n\n"
-						+ Zotero.getString('general.seeForMoreInformation', kbURL),
-						false, noReloadOnFailure);
-				}
-				else if ((secInfo.securityState & Ci.nsIWebProgressListener.STATE_IS_BROKEN) == Ci.nsIWebProgressListener.STATE_IS_BROKEN) {
-					_error(Zotero.getString('sync.error.sslConnectionError'), false, noReloadOnFailure);
 				}
 			}
 			if (xmlhttp.status === 0) {