diff --git a/modules/themeManager.js b/modules/themeManager.js
index e790c374..f884ffeb 100644
--- a/modules/themeManager.js
+++ b/modules/themeManager.js
@@ -37,16 +37,75 @@ const EXPORTED_SYMBOLS = ['TreeStyleTabThemeManager'];
 
 Components.utils.import('resource://treestyletab-modules/utils.js');
 
-var TreeStyleTabThemeManager = {
-	preLoadImagesForStyle : function(aStyle)
+function TreeStyleTabThemeManager(aWindow)
+{
+	this.window = aWindow;
+	this._preLoadImagesForStyleDone = [];
+	this._preLoadImagesForStyleDoneImages = [];
+}
+TreeStyleTabThemeManager.prototype = {
+	destroy : function()
 	{
+		delete this.window;
+	},
+
+	set : function(aStyle, aPosition)
+	{
+		if (this._lastStyles)
+			this._lastStyles.forEach(function(aStyle) {
+				aStyle.parentNode.removeChild(aStyle);
+			});
+		this._lastStyles = null;
+
+		var styles = [];
+		switch (aStyle)
+		{
+			case 'default':
+			default:
+
+			case 'flat':
+			case 'mixed':
+				styles.push('chrome://treestyletab/skin/square/square.css');
+				styles.push('chrome://treestyletab/skin/square/dropshadow.css');
+				break;
+
+			case 'vertigo':
+				styles.push('chrome://treestyletab/skin/square/square.css');
+				break;
+
+			case 'metal':
+				styles.push('chrome://treestyletab/skin/metal/metal.css');
+				break;
+
+			case 'sidebar':
+				styles.push('chrome://treestyletab/skin/sidebar/sidebar.css');
+				break;
+		}
+
+		if (styles.length) {
+			this._lastStyles = styles.map(function(aStyle) {
+				var d = this.window.document;
+				var pi = d.createProcessingInstruction(
+							'xml-stylesheet',
+							'type="text/css" href="'+aStyle+'"'
+						);
+				d.insertBefore(pi, d.documentElement);
+				return pi;
+			}, this);
+			this.preloadImages(aStyle, aPosition);
+		}
+	},
+
+	preloadImages : function(aStyle, aPosition)
+	{
+		var key = aStyle+'-'+aPosition;
 		if (!aStyle ||
-			this._preLoadImagesForStyleDone.indexOf(aStyle) > -1)
+			this._preLoadImagesForStyleDone.indexOf(key) > -1)
 			return;
-		this._preLoadImagesForStyleDone.push(aStyle);
+		this._preLoadImagesForStyleDone.push(key);
 
 		var images = aStyle in this._preLoadImages ?
-				this._preLoadImages[aStyle] :
+				this._preLoadImages[key] :
 				null ;
 		if (!images) return;
 
@@ -54,12 +113,11 @@ var TreeStyleTabThemeManager = {
 			if (this._preLoadImagesForStyleDoneImages.indexOf(aImage) > -1)
 				return;
 
-			(new Image()).src = aImage;
+			(new this.window.Image()).src = aImage;
 			this._preLoadImagesForStyleDoneImages.push(aImage);
 		}, this);
 	},
-	_preLoadImagesForStyleDone : [],
-	_preLoadImagesForStyleDoneImages : [],
+
 	_preLoadImages : {
 		'metal-left' : [
 			'chrome://treestyletab/skin/metal/tab-active-l.png',
diff --git a/modules/window.js b/modules/window.js
index 1a534e5d..5d148a0f 100644
--- a/modules/window.js
+++ b/modules/window.js
@@ -46,11 +46,6 @@ XPCOMUtils.defineLazyGetter(this, 'TreeStyleTabBrowser', function() {
 	Components.utils.import('resource://treestyletab-modules/browser.js', ns);
 	return ns.TreeStyleTabBrowser;
 });
-XPCOMUtils.defineLazyGetter(this, 'TreeStyleTabThemeManager', function() {
-	var ns = {};
-	Components.utils.import('resource://treestyletab-modules/themeManager.js', ns);
-	return ns.TreeStyleTabThemeManager;
-});
  
 function TreeStyleTabWindow(aWindow) 
 {
@@ -262,6 +257,26 @@ TreeStyleTabWindow.prototype = {
 				) :
 				this.getTreePref('tabbar.autoHide.mode');
 	},
+ 
+	get autoHideWindow() 
+	{
+		if (!this._autoHideWindow) {
+			let ns = {};
+			Components.utils.import('resource://treestyletab-modules/autoHide.js', ns);
+			this._autoHideWindow = new ns.AutoHideWindow(this.window);
+		}
+		return this._autoHideWindow;
+	},
+ 
+	get themeManager() 
+	{
+		if (!this._themeManager) {
+			let ns = {};
+			Components.utils.import('resource://treestyletab-modules/themeManager.js', ns);
+			this._themeManager = new ns.TreeStyleTabThemeManager(this.window);
+		}
+		return this._themeManager;
+	},
   
 /* Initializing */ 
 	
@@ -280,6 +295,9 @@ TreeStyleTabWindow.prototype = {
 		w.TreeStyleTabWindowHelper.preInit();
 
 		this.migratePrefs();
+
+		// initialize theme
+		this.onPrefChange('extensions.treestyletab.tabbar.style');
 	},
 	preInitialized : false,
 	
@@ -393,7 +411,11 @@ TreeStyleTabWindow.prototype = {
 		w.removeEventListener('load', this, false);
 		w.addEventListener('unload', this, false);
 
-		if (!this.browser) return;
+		if (
+			w.location.href.indexOf('chrome://browser/content/browser.xul') != 0 ||
+			!this.browser
+			)
+			return;
 
 		if (this.initialized) return;
 		this.initialized = true;
@@ -432,7 +454,6 @@ TreeStyleTabWindow.prototype = {
 		// Init autohide service only if it have to be activated.
 		if (this.isAutoHide)
 			this.onPrefChange('extensions.treestyletab.tabbar.autoHide.mode');
-		this.onPrefChange('extensions.treestyletab.tabbar.style');
 		this.onPrefChange('extensions.treestyletab.autoCollapseExpandSubtreeOnSelect.whileFocusMovingByShortcut');
 	},
 	initialized : false,
@@ -535,6 +556,12 @@ TreeStyleTabWindow.prototype = {
 				let w = this.window;
 				w.removeEventListener('unload', this, false);
 
+				this.autoHideWindow.destroy();
+				delete this._autoHideWindow;
+
+				this.themeManager.destroy();
+				delete this._themeManager;
+
 				this.browser.treeStyleTab.saveCurrentState();
 				this.destroyTabBrowser(this.browser);
 
@@ -1171,16 +1198,6 @@ TreeStyleTabWindow.prototype = {
 		}
 	},
  
-	get autoHideWindow() 
-	{
-		if (!this._autoHideWindow) {
-			let ns = {};
-			Components.utils.import('resource://treestyletab-modules/autoHide.js', ns);
-			this._autoHideWindow = new ns.AutoHideWindow(this.window);
-		}
-		return this._autoHideWindow;
-	},
- 
 	toggleAutoHide : function TSTWindow_toggleAutoHide(aTabBrowser) /* PUBLIC API, for backward compatibility */ 
 	{
 		this.autoHideWindow.toggleMode(aTabBrowser || this.browser);
@@ -1570,10 +1587,7 @@ TreeStyleTabWindow.prototype = {
 
 			case 'extensions.treestyletab.tabbar.style':
 			case 'extensions.treestyletab.tabbar.position':
-				TreeStyleTabThemeManager.preLoadImagesForStyle([
-					this.getPref('extensions.treestyletab.tabbar.style'),
-					this.position
-				].join('-'));
+				this.themeManager.set(this.getPref('extensions.treestyletab.tabbar.style'), this.position);
 				break;
 
 			case 'browser.ctrlTab.previews':
diff --git a/skin/classic/treestyletab/square/square.css b/skin/classic/treestyletab/square/square.css
index bf5b85ba..7db444c1 100644
--- a/skin/classic/treestyletab/square/square.css
+++ b/skin/classic/treestyletab/square/square.css
@@ -1,3 +1,5 @@
 @import url("base.css");
 @import url("tab-surface.css");
-
+/* dynamically applied by themeManager.js
+@import url("dropshadow.css");
+*/
diff --git a/skin/classic/treestyletab/treestyletab.css b/skin/classic/treestyletab/treestyletab.css
index e0c2fcbc..9ddff5b4 100644
--- a/skin/classic/treestyletab/treestyletab.css
+++ b/skin/classic/treestyletab/treestyletab.css
@@ -1,8 +1,9 @@
 @import url("base.css");
+/* dynamically applied by themeManager.js
 @import url("square/square.css");
-@import url("square/dropshadow.css");
 @import url("metal/metal.css");
 @import url("sidebar/sidebar.css");
+*/
 
 @import url("ui.css");