diff --git a/chrome/content/zotero/overlay.js b/chrome/content/zotero/overlay.js
index 0abc5b8a5..8dffd00db 100644
--- a/chrome/content/zotero/overlay.js
+++ b/chrome/content/zotero/overlay.js
@@ -34,6 +34,9 @@ var ZoteroOverlay = new function()
 	this.isTab = false;
 	
 	this.onLoad = function() {
+		ZoteroPane_Overlay = ZoteroPane;
+		ZoteroPane.init();
+		
 		var appInfo = Components.classes["@mozilla.org/xre/app-info;1"]
 						.getService(Components.interfaces.nsIXULAppInfo);
 		isFx36 = appInfo.platformVersion.indexOf('1.9') === 0;
@@ -134,9 +137,6 @@ var ZoteroOverlay = new function()
 			setTimeout("gBrowser.selectedTab = gBrowser.addTab(Zotero.initialURL); Zotero.initialURL = null;", 1);
 		}
 		
-		ZoteroPane_Overlay = ZoteroPane;
-		ZoteroPane.init();
-		
 		// Hide browser chrome on Zotero tab
 		if(Zotero.isFx4) {
 			XULBrowserWindow.inContentWhitelist.push("chrome://zotero/content/tab.xul");
@@ -272,7 +272,7 @@ var ZoteroOverlay = new function()
 		for(var index = 0; index < numTabs; index++) {
 			var currentBrowser = gBrowser.getBrowserAtIndex(index);
 			if(ZOTERO_TAB_URL == currentBrowser.currentURI.spec) {
-				tab = gBrowser.tabs[index];
+				tab = (gBrowser.tabs ? gBrowser.tabs : gBrowser.mTabs)[index];
 				break;
 			}
 		}
@@ -303,7 +303,7 @@ var ZoteroOverlay = new function()
 		if(tab) {		// Zotero is running in a tab
 			if(setMode) return;
 			// don't do anything if Zotero tab is the only tab
-			if(tab && gBrowser.tabs.length === 1) return;
+			if(tab && (gBrowser.tabs ? gBrowser.tabs : gBrowser.mTabs).length === 1) return;
 			
 			// swap ZoteroPane object
 			ZoteroPane = ZoteroPane_Overlay;
diff --git a/chrome/content/zotero/tab.js b/chrome/content/zotero/tab.js
index 481e19452..65a2de89b 100644
--- a/chrome/content/zotero/tab.js
+++ b/chrome/content/zotero/tab.js
@@ -47,7 +47,7 @@ var ZoteroTab = new function()
 			
 			var currentBrowser = window.gBrowser.browsers[index];
 			if(currentBrowser && ZOTERO_TAB_URL == currentBrowser.currentURI.spec) {
-				window.gBrowser.removeTab(window.gBrowser.tabs[index]);
+				window.gBrowser.removeTab((window.gBrowser.tabs ? window.gBrowser.tabs : window.gBrowser.mTabs)[index]);
 			}
 		}
 		
@@ -64,15 +64,16 @@ var ZoteroTab = new function()
 			}, false);
 		}
 		
-		var browser = window.gBrowser.getBrowserForDocument(document);
-		if(window.gBrowser.selectedBrowser === browser) {
+		// get tab for browser
+		var tab = (window.gBrowser.tabs ? window.gBrowser.tabs : window.gBrowser.mTabs)[browserIndex];
+		if(window.gBrowser.selectedTab === tab) {
 			// if tab is already selected, init now
 			ZoteroPane.init();
 			ZoteroPane.makeVisible();
 		} else {
 			// otherwise, add a handler to wait until this tab is selected
 			var listener = function(event) {
-				if(window.gBrowser.getBrowserForTab(event.target) !== browser) return;
+				if(event.target !== tab) return;
 				window.gBrowser.tabContainer.removeEventListener("TabSelect", listener, false);
 				ZoteroPane.init();
 				ZoteroPane.makeVisible();
@@ -81,7 +82,6 @@ var ZoteroTab = new function()
 		}
 		
 		if(Zotero && Zotero.isFx4) {
-			var tab = window.gBrowser.tabs[browserIndex];
 			// on Fx 4, add an event listener so the pinned tab isn't restored on close
 			var pinnedTabCloser = function() {
 				try {