diff --git a/content/treestyletab/bookmarksOverlay.xul b/content/treestyletab/bookmarksOverlay.xul
index d68acf73..9db89e4d 100644
--- a/content/treestyletab/bookmarksOverlay.xul
+++ b/content/treestyletab/bookmarksOverlay.xul
@@ -1,6 +1,5 @@
 <?xml version="1.0"?>
 <overlay xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
-<script src="res/boxObject.js" type="application/x-javascript; version=1.7"/>
 <script src="res/stringBundle.js" type="application/x-javascript; version=1.7"/>
 <script src="res/animationManager.js" type="application/x-javascript; version=1.7"/>
 <script src="treestyletab.js" type="application/x-javascript; version=1.7"/>
diff --git a/content/treestyletab/res/stringBundle.js b/content/treestyletab/res/stringBundle.js
index 5c71166d..b636e5b8 100644
--- a/content/treestyletab/res/stringBundle.js
+++ b/content/treestyletab/res/stringBundle.js
@@ -2,7 +2,6 @@
  string bundle utility
 
  Usage:
-   // use instead of HTMLDocument.getBoxObjectFor(HTMLElement)
    var bundle = window['piro.sakura.ne.jp']
                          .stringBundle
                          .get('chrome://example/locale/example.properties');
diff --git a/content/treestyletab/treestyletab.js b/content/treestyletab/treestyletab.js
index 497fb289..74cfb75a 100644
--- a/content/treestyletab/treestyletab.js
+++ b/content/treestyletab/treestyletab.js
@@ -111,11 +111,6 @@ var TreeStyleTabService = {
 			);
 	},
   
-	getBoxObjectFor : function TSTService_getBoxObjectFor(aNode) 
-	{
-		return window['piro.sakura.ne.jp'].boxObject.getBoxObjectFor(aNode);
-	},
- 
 	getPropertyPixelValue : function TSTService_getPropertyPixelValue(aElementOrStyle, aProp) 
 	{
 		var style = aElementOrStyle instanceof Components.interfaces.nsIDOMCSSStyleDeclaration ?
diff --git a/content/treestyletab/treestyletab.xul b/content/treestyletab/treestyletab.xul
index 3647fad1..3caf108b 100644
--- a/content/treestyletab/treestyletab.xul
+++ b/content/treestyletab/treestyletab.xul
@@ -7,7 +7,6 @@
 <overlay id="treestyletab-overlay"
          xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
 
-<script src="res/boxObject.js" type="application/x-javascript; version=1.7"/>
 <script src="res/stringBundle.js" type="application/x-javascript; version=1.7"/>
 <script src="res/autoScroll.js" type="application/x-javascript; version=1.7"/>
 <script src="res/animationManager.js" type="application/x-javascript; version=1.7"/>
diff --git a/content/treestyletab/res/boxObject.js b/modules/boxObject.js
similarity index 95%
rename from content/treestyletab/res/boxObject.js
rename to modules/boxObject.js
index 7c1a4c2c..2c02a8e8 100644
--- a/content/treestyletab/res/boxObject.js
+++ b/modules/boxObject.js
@@ -1,3 +1,6 @@
+var EXPORTED_SYMBOLS = ['window'];
+var window = {};
+
 /*
  "getBoxObjectFor()" compatibility library for Firefox 3.6 or later
 
diff --git a/modules/utils.js b/modules/utils.js
index 1e8fe21b..22726b53 100644
--- a/modules/utils.js
+++ b/modules/utils.js
@@ -38,6 +38,12 @@ var EXPORTED_SYMBOLS = ['TreeStyleTabUtils'];
 var Cc = Components.classes;
 var Ci = Components.interfaces;
  
+var prefs = {}; 
+Components.utils.import('resource://treestyletab-modules/prefs.js', prefs);
+
+var boxObject = {}; 
+Components.utils.import('resource://treestyletab-modules/boxObject.js', boxObject);
+ 
 var TreeStyleTabUtils = { 
 	
 /* attributes */ 
@@ -253,6 +259,11 @@ var TreeStyleTabUtils = {
  
 /* utilities */ 
 	
+	getBoxObjectFor : function TSTUtils_getBoxObjectFor(aNode) 
+	{
+		return boxObject.window['piro.sakura.ne.jp'].boxObject.getBoxObjectFor(aNode);
+	},
+ 
 	get browserWindow() 
 	{
 		return this.WindowMediator.getMostRecentWindow('navigator:browser');
@@ -1397,6 +1408,5 @@ var TreeStyleTabUtils = {
   
 }; 
  
-Components.utils.import('resource://treestyletab-modules/prefs.js'); 
-TreeStyleTabUtils.__proto__ = window['piro.sakura.ne.jp'].prefs;
+TreeStyleTabUtils.__proto__ = prefs.window['piro.sakura.ne.jp'].prefs;