backout part of previous push

browser/base/content/tabbrowser.xml

@@ -2236,7 +2236,7 @@
             this.mTabContainer.childNodes[i]._selected = false;
           }
           this.mCurrentTab._selected = true;
-          this.mTabContainer.mTabstrip.ensureElementIsVisible(this.mCurrentTab, false);
+          this.mTabContainer.mTabstrip.scrollBoxObject.ensureElementIsVisible(this.mCurrentTab);
 
           var evt = document.createEvent("UIEvents");
           evt.initUIEvent("TabMove", true, false, window, oldPosition);
@@ -2795,7 +2795,7 @@
          this._scrollButtonDownBox.collapsed = false;
          this._scrollButtonDownBoxAnimate.collapsed = false;
 #endif
-         this.ensureElementIsVisible(tabs.selectedItem, false);
+         this.scrollBoxObject.ensureElementIsVisible(tabs.selectedItem);
       ]]></handler>
 
 #ifdef XP_MACOSX