The Tor Browser / file revision

 function test() {

   for (let i = 0; i < 9; i++)

     gBrowser.addTab();

   var isLinux = navigator.platform.indexOf("Linux") == 0;

   for (let i = 9; i >= 1; i--) {

     EventUtils.synthesizeKey(i.toString(), { altKey: isLinux, accelKey: !isLinux });

     is(gBrowser.tabContainer.selectedIndex, (i == 9 ? gBrowser.tabs.length : i) - 1,

        (isLinux ? "Alt" : "Accel") + "+" + i + " selects expected tab");

   }

   gBrowser.selectTabAtIndex(-3);

   is(gBrowser.tabContainer.selectedIndex, gBrowser.tabs.length - 3,

      "gBrowser.selectTabAtIndex(-3) selects expected tab");

   for (let i = 0; i < 9; i++)

     gBrowser.removeCurrentTab();

 }