diff --git a/content/treestyletab/treestyletab.js b/content/treestyletab/treestyletab.js
index 54ebb279..abaf0248 100644
--- a/content/treestyletab/treestyletab.js
+++ b/content/treestyletab/treestyletab.js
@@ -112,25 +112,15 @@ var TreeStyleTabService = {
 	maxTabbarWidth : function TSTService_maxTabbarWidth(aWidth, aTabBrowser) 
 	{
 		aTabBrowser = aTabBrowser || this.browser;
-		return Math.min(
-				aWidth,
-				parseInt(Math.min(
-					Math.max(window.outerWidth, parseInt(document.documentElement.getAttribute('width'))),
-					aTabBrowser.boxObject.width
-				) * 0.9)
-			);
+		var max = Math.max(window.outerWidth, parseInt(document.documentElement.getAttribute('width') || 0));
+		return Math.min(aWidth, max * 0.7);
 	},
  
 	maxTabbarHeight : function TSTService_maxTabbarHeight(aHeight, aTabBrowser) 
 	{
 		aTabBrowser = aTabBrowser || this.browser;
-		return Math.min(
-				aHeight,
-				parseInt(Math.min(
-					Math.max(window.outerHeight, parseInt(document.documentElement.getAttribute('height'))),
-					aTabBrowser.boxObject.height
-				) * 0.9)
-			);
+		var max = Math.max(window.outerHeight, parseInt(document.documentElement.getAttribute('height') || 0));
+		return Math.min(aHeight, max * 0.7);
 	},
   
 /* Initializing */ 
diff --git a/modules/utils.js b/modules/utils.js
index 160c4338..50014818 100644
--- a/modules/utils.js
+++ b/modules/utils.js
@@ -1725,6 +1725,8 @@ var TreeStyleTabUtils = {
 		var shrunken = this.getTreePref('tabbar.shrunkenWidth');
 		if (expanded <= shrunken) {
 			this.tabbarWidthResetting = true;
+			var w = this.browserWindow;
+			if (w) expanded = Math.min(expanded, w.outerWidth);
 			if (aPrefName == 'extensions.treestyletab.tabbar.width')
 				this.setTreePref('tabbar.shrunkenWidth', parseInt(expanded / 1.5));
 			else