Add "Check for Update" button to error alert when DB version is newer

chrome/content/zotero/xpcom/zotero.js

@@ -639,6 +639,56 @@ Components.utils.import("resource://gre/modules/Services.jsm");
 						+ Zotero.getString('startupError.zoteroVersionIsOlder.current', Zotero.version) + "\n\n"
 						+ Zotero.getString('general.seeForMoreInformation', kbURL);
 					Zotero.startupError = msg;
+					_startupErrorHandler = function() {
+						var ps = Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
+							.getService(Components.interfaces.nsIPromptService);
+						var buttonFlags = (ps.BUTTON_POS_0) * (ps.BUTTON_TITLE_IS_STRING)
+							+ (ps.BUTTON_POS_1) * (ps.BUTTON_TITLE_OK)
+							+ ps.BUTTON_POS_0_DEFAULT;
+						
+						var index = ps.confirmEx(null, "", Zotero.startupError, buttonFlags,
+							Zotero.getString('general.checkForUpdate'), null, null,
+							null, {});
+						
+						// "Check for updates" button
+						if(index === 0) {
+							if(Zotero.isStandalone) {
+								ZoteroStandalone.checkForUpdates();
+							} else {
+								// In Firefox, show the add-on manager
+								Components.utils.import("resource://gre/modules/AddonManager.jsm");
+								AddonManager.getAddonByID(ZOTERO_CONFIG['GUID'],
+									function (addon) {
+										// Disable auto-update so that the user is presented with the option
+										var initUpdateState = addon.applyBackgroundUpdates;
+										addon.applyBackgroundUpdates = AddonManager.AUTOUPDATE_DISABLE;
+										addon.findUpdates({
+												onNoUpdateAvailable: function() {
+													ps.alert(null, '', Zotero.getString('zotero.preferences.update.upToDate'));
+												},
+												onUpdateAvailable: function() {
+													// Show available update
+													Components.classes["@mozilla.org/appshell/window-mediator;1"]
+														.getService(Components.interfaces.nsIWindowMediator)
+														.getMostRecentWindow('navigator:browser')
+														.BrowserOpenAddonsMgr('addons://updates/available');
+												},
+												onUpdateFinished: function() {
+													// Restore add-on auto-update state, but don't fire
+													//  too quickly or the update will not show in the
+													//  add-on manager
+													setTimeout(function() {
+															addon.applyBackgroundUpdates = initUpdateState;
+													}, 1000);
+												}
+											},
+											AddonManager.UPDATE_WHEN_USER_REQUESTED
+										);
+									}
+								);
+							}
+						}
+					};
 				}
 				else {
 					Zotero.startupError = Zotero.getString('startupError.databaseUpgradeError') + "\n\n" + e;