diff --git a/content/treestyletab/hacks.js b/content/treestyletab/hacks.js
index 2ced9b4c..76f52913 100644
--- a/content/treestyletab/hacks.js
+++ b/content/treestyletab/hacks.js
@@ -258,6 +258,52 @@ TreeStyleTabService.overrideExtensionsOnInitBefore = function TSTService_overrid
 		);
 	}
 
+	// Tabberwocky
+	// https://addons.mozilla.org/firefox/addon/14439
+	if ('tabberwocky' in window) {
+		TreeStyleTabBrowser.prototype.isMultiRow = function()
+		{
+			return this.getPref('tabberwocky.multirow') && !this.isVertical;
+		};
+
+		let listener = {
+				handleEvent : function(aEvent)
+				{
+					switch (aEvent.type)
+					{
+						case 'TreeStyleTabTabbarPositionChanged':
+							var b = aEvent.originalTarget;
+							if (b.treeStyleTab.isVertical)
+								b.treeStyleTab.setPref('tabberwocky.multirow', false);
+							break;
+
+						case 'unload':
+							window.removeEventListener('TreeStyleTabTabbarPositionChanged', this, false);
+							window.removeEventListener('unload', this, false);
+							break;
+					}
+				}
+			};
+		window.addEventListener('TreeStyleTabTabbarPositionChanged', listener, false);
+		window.addEventListener('unload', listener, false);
+
+		if ('openSelectedLinks' in tabberwocky) {
+			eval('tabberwocky.openSelectedLinks = '+
+				tabberwocky.openSelectedLinks.toSource().replace(
+					'links.forEach(',
+					<![CDATA[
+						TreeStyleTabService.readyToOpenChildTab(aFrame, true)
+					$&]]>
+				).replace(
+					/(\}\)?)$/,
+					<![CDATA[
+						TreeStyleTabService.stopToOpenChildTab(aFrame)
+					$1]]>
+				)
+			);
+		}
+	}
+
 };
 
 TreeStyleTabService.overrideExtensionsOnInitAfter = function TSTService_overrideExtensionsOnInitAfter() {
@@ -932,36 +978,6 @@ TreeStyleTabService.overrideExtensionsOnInitAfter = function TSTService_override
 		}
 	}
 
-	// Tabberwocky
-	// https://addons.mozilla.org/firefox/addon/14439
-	if ('multirow' in window &&
-		'updateMultiRowTabs' in multirow) {
-		eval('multirow.updateMultiRowTabs = '+
-			multirow.updateMultiRowTabs.toSource().replace(
-				'gBrowser.mPrefs.getBoolPref("tabberwocky.multirow")',
-				'$& && !gBrowser.treeStyleTab.isVertical'
-			)
-		);
-		window.setTimeout('multirow.updateMultiRowTabs();', 0);
-	}
-	if ('tabberwocky' in window) {
-		if ('openSelectedLinks' in tabberwocky) {
-			eval('tabberwocky.openSelectedLinks = '+
-				tabberwocky.openSelectedLinks.toSource().replace(
-					'links.forEach(',
-					<![CDATA[
-						TreeStyleTabService.readyToOpenChildTab(aFrame, true)
-					$&]]>
-				).replace(
-					/(\}\)?)$/,
-					<![CDATA[
-						TreeStyleTabService.stopToOpenChildTab(aFrame)
-					$1]]>
-				)
-			);
-		}
-	}
-
 	window.setTimeout(function(aSelf) {
 		aSelf.overrideExtensionsDelayed();
 	}, 0, this);
diff --git a/content/treestyletab/treestyletabbrowser.js b/content/treestyletab/treestyletabbrowser.js
index 8ab9c6dc..35cce488 100644
--- a/content/treestyletab/treestyletabbrowser.js
+++ b/content/treestyletab/treestyletabbrowser.js
@@ -148,6 +148,9 @@ TreeStyleTabBrowser.prototype = {
 			}
 		}
 
+		let position = this.currentTabbarPosition;
+		this.fireTabbarPositionEvent('TreeStyleTabTabbarPositionChanging', 'top', position); /* PUBLIC API */
+
 		this.initTabbar();
 
 		b.addEventListener('TabOpen',        this, true);
@@ -583,6 +586,8 @@ TreeStyleTabBrowser.prototype = {
 
 		this.autoHide;
 
+		this.fireTabbarPositionEvent('TreeStyleTabTabbarPositionChanged', 'top', position); /* PUBLIC API */
+
 		b = null;
 	},
 	
@@ -1059,6 +1064,17 @@ TreeStyleTabBrowser.prototype = {
 			}
 		}, 100);
 	},
+ 
+	fireTabbarPositionEvent : function TSTBrowser_fireTabbarPositionEvent(aType, aOldPosition, aNewPosition) 
+	{
+		if (aOldPosition == aNewPosition) return;
+
+		var event = document.createEvent('Events');
+		event.initEvent(aType, true, true);
+		event.oldPosition = aOldPosition;
+		event.newPosition = aNewPosition;
+		this.mTabBrowser.dispatchEvent(event);
+	},
    
 	destroy : function TSTBrowser_destroy() 
 	{
@@ -1174,14 +1190,7 @@ TreeStyleTabBrowser.prototype = {
 		{
 			case 'extensions.treestyletab.tabbar.position':
 				var oldPosition = b.getAttribute(this.kTABBAR_POSITION);
-				let (event) {
-					/* PUBLIC API */
-					event = document.createEvent('Events');
-					event.initEvent('TreeStyleTabTabbarPositionChanging', true, true);
-					event.oldPosition = oldPosition;
-					event.newPosition = value;
-					this.mTabBrowser.dispatchEvent(event);
-				}
+				this.fireTabbarPositionEvent('TreeStyleTabTabbarPositionChanging', oldPosition, value); /* PUBLIC API */
 				this.initTabbar();
 				tabs.forEach(function(aTab) {
 					this.initTabAttributes(aTab);
@@ -1189,14 +1198,7 @@ TreeStyleTabBrowser.prototype = {
 				tabs.forEach(function(aTab) {
 					this.initTabContents(aTab);
 				}, this);
-				let (event) {
-					/* PUBLIC API */
-					event = document.createEvent('Events');
-					event.initEvent('TreeStyleTabTabbarPositionChanged', true, true);
-					event.oldPosition = oldPosition;
-					event.newPosition = value;
-					this.mTabBrowser.dispatchEvent(event);
-				}
+				this.fireTabbarPositionEvent('TreeStyleTabTabbarPositionChanged', oldPosition, value); /* PUBLIC API */
 				window.setTimeout(function(aSelf) {
 					aSelf.checkTabsIndentOverflow();
 				}, 0, this);
@@ -1698,7 +1700,12 @@ TreeStyleTabBrowser.prototype = {
 			if (
 				nextFocusedTab &&
 				this._tabFocusAllowance.every(function(aFunc) {
-					return aFunc.call(this, b);
+					try {
+						return aFunc.call(this, b);
+					}
+					catch(e) {
+						return false;
+					}
 				}, this)
 				)
 				b.selectedTab = nextFocusedTab;