code: function tabBrowser_waitForTabPanel(tabIndex, elemString) {
      // Get the specified tab panel element
      var tabPanel = this.getTabPanelElement(tabIndex, elemString);
      
      // Get the style information for the tab panel element
      var style = this._controller.window.getComputedStyle(tabPanel.getNode(), null);
      
      // Wait for the top margin to be 0px - ie. has stopped animating
      // XXX: A notification bar starts at a negative pixel margin and drops down
      //      to 0px.  This creates a race condition where a test may click
      //      before the notification bar appears at it's anticipated screen location
      this._controller.waitFor(function () {
        return style.marginTop == '0px';
      }, "Expected notification bar to be visible: '" + elemString + "' ");
    }
docs: Waits for a particular tab panel element to display and stop animating
  
  @param {number} tabIndex
  Index of the tab to check
  @param {string} elemString
  Lookup string of the tab panel element