fix for bug #343370. additional scenario where tab scrolling does not handle window resize well. cache the tab strip width and only adjust the tabstrip, scroll and ensure the selected tab is visible if the width changes. r=asaf

browser/base/content/tabbrowser.xml

@@ -2414,14 +2414,21 @@
 
           var self = this;
           function onResize() {
-            self.adjustTabstrip(false);
+            var width = self.mTabstrip.boxObject.width;
-            self.mTabstrip.scrollBoxObject
+            if (width != self.mTabstripWidth) {
-                          .ensureElementIsVisible(self.selectedItem);
+              self.adjustTabstrip(false);
+              self.mTabstrip.scrollByIndex(1);
+              self.mTabstrip.scrollBoxObject
+                            .ensureElementIsVisible(self.selectedItem);
+              self.mTabstripWidth = width;
+            }
           }
           window.addEventListener("resize", onResize, false);
         ]]>
       </constructor>
 
+      <field name="mTabstripWidth">0</field>
+
       <field name="mTabstrip">
         document.getAnonymousElementByAttribute(this, "anonid", "arrowscrollbox");
       </field>
@@ -2563,7 +2570,7 @@
     <handlers>
       <handler event="TabOpen"   action="this.adjustTabstrip(false);"/>
       <handler event="TabClose"  action="this.adjustTabstrip(true);"/>
-      <handler event="TabSelect" action="this._handleTabSelect()"/>
+      <handler event="TabSelect" action="this._handleTabSelect();"/>
     </handlers>
   </binding>