diff --git a/content/treestyletab/windowHelper.js b/content/treestyletab/windowHelper.js
index bd6b3b9f..e0bca8f5 100644
--- a/content/treestyletab/windowHelper.js
+++ b/content/treestyletab/windowHelper.js
@@ -284,8 +284,8 @@ var TreeStyleTabWindowHelper = {
 
 		TreeStyleTabUtils.doPatching(FullScreen.toggle, 'FullScreen.toggle', function(aName, aSource) {
 			return eval(aName+' = '+aSource.replace(
-				'{',
-				'{ gBrowser.treeStyleTab.onBeforeFullScreenToggle(); '
+				'if (enterFS) {',
+				'gBrowser.treeStyleTab.onBeforeFullScreenToggle(enterFS); $&'
 			));
 		}, 'treeStyleTab');
 
diff --git a/modules/browser.js b/modules/browser.js
index d91f39d2..a571f16b 100644
--- a/modules/browser.js
+++ b/modules/browser.js
@@ -5120,17 +5120,16 @@ TreeStyleTabBrowser.prototype = inherit(TreeStyleTabWindow.prototype, {
 		}).bind(this), 0);
 	},
  
-	onBeforeFullScreenToggle : function TSTBrowser_onBeforeFullScreenToggle() 
+	onBeforeFullScreenToggle : function TSTBrowser_onBeforeFullScreenToggle(aEnterFS)
 	{
 		if (this.position != 'top') {
-			var isEnteringFullScreenMode = !this.window.fullScreen;
 			// entering to the DOM-fullscreen (ex. YouTube Player)
-			if (this.document.mozFullScreen && isEnteringFullScreenMode) {
+			if (this.document.mozFullScreen) {
 				this.setTabbrowserAttribute(this.kDOM_FULLSCREEN_ACTIVATED, true);
 			}
 			else {
 				if (this.document.documentElement.getAttribute(this.kDOM_FULLSCREEN_ACTIVATED) != 'true') {
-					if (isEnteringFullScreenMode)
+					if (aEnterFS)
 						this.autoHide.startForFullScreen();
 					else
 						this.autoHide.endForFullScreen();