The Tor Browser / file revision

 /* Any copyright is dedicated to the Public Domain.

    http://creativecommons.org/publicdomain/zero/1.0/ */

 function test() {

   waitForExplicitFinish();

   newWindowWithTabView(function (win) {

     registerCleanupFunction(function () win.close());

     let cw = win.TabView.getContentWindow();

     let groupItem = cw.GroupItems.groupItems[0];

     // create some tabs with favIcons

     for (let i = 0; i < 3; i++)

       win.gBrowser.loadOneTab("http://mochi.test:8888/browser/browser/components/tabview/test/test_bug644097.html", {inBackground: true});

     win.gBrowser.removeTab(win.gBrowser.tabs[0]);

     // shrink the group until it stacks

     let size = 400;

     while (!groupItem.isStacked() && --size)

       groupItem.setSize(size, size, true);

     // determine the tabItem at the top of the stack

     let tabItem;

     groupItem.getChildren().forEach(function (item) {

       if (groupItem.isTopOfStack(item))

         tabItem = item;

     });

     ok(tabItem, "we found the tabItem at the top of the stack");

     let fav = tabItem.$fav;

     is(fav.css("display"), "block", "the favIcon is visible");

     is(fav.css("left"), "0px", "the favIcon is at the left-most position");

     is(fav.css("top"), "0px", "the favIcon is at the top-most position");

     finish();

   });

 }