gecko/browser/base/content/test/browser_ctrlTab.js

function test() {
  while (gBrowser.mTabs.length > 1)
    gBrowser.removeCurrentTab();

  gBrowser.addTab();
  gBrowser.addTab();
  gBrowser.addTab();

  ctrlTabTest([2]      , 1, 0);
  ctrlTabTest([2, 3, 1], 2, 2);
  ctrlTabTest([]       , 4, 2);

  gBrowser.removeTab(gBrowser.tabContainer.lastChild);

  ctrlTabTest([2, 1, 0], 7, 1);

  gBrowser.removeTab(gBrowser.tabContainer.lastChild);

  ctrlTabTest([1]      , 1, 0);

  gBrowser.removeTab(gBrowser.tabContainer.lastChild);

  var focusedWindow = document.commandDispatcher.focusedWindow;
  var eventConsumed = true;
  var detectKeyEvent = function (event) {
    eventConsumed = event.getPreventDefault();
  };
  document.addEventListener("keypress", detectKeyEvent, false);
  pressCtrlTab();
  document.removeEventListener("keypress", detectKeyEvent, false);
  ok(eventConsumed, "Ctrl+Tab consumed by the tabbed browser if one tab is open");
  is(focusedWindow.location, document.commandDispatcher.focusedWindow.location,
     "Ctrl+Tab doesn't change focus if one tab is open");


  /* private utitily functions */
  function pressCtrlTab()
    EventUtils.synthesizeKey("VK_TAB", { ctrlKey: true });

  function releaseCtrl()
    EventUtils.synthesizeKey("VK_CONTROL", { type: "keyup" });

  function ctrlTabTest(tabsToSelect, tabTimes, expectedIndex) {
    tabsToSelect.forEach(function (index) {
      gBrowser.selectedTab = gBrowser.mTabs[index];
    });

    var indexStart = gBrowser.tabContainer.selectedIndex;
    var tabCount = gBrowser.mTabs.length;
    var normalized = tabTimes % tabCount;
    var where = normalized == 1 ? "back to the previously selected tab" :
                normalized + " tabs back in most-recently-selected order";

    for (let i = 0; i < tabTimes; i++) {
      pressCtrlTab();

      if (tabCount > 2)
       is(gBrowser.tabContainer.selectedIndex, indexStart,
         "Selected tab doesn't change while tabbing");
    }

    if (tabCount > 2) {
      ok(ctrlTab.panel.state == "showing" || ctrlTab.panel.state == "open",
         "With " + tabCount + " tabs open, Ctrl+Tab opens the preview panel");

      is(ctrlTab.label.value, gBrowser.mTabs[expectedIndex].label,
         "Preview panel displays label of expected tab");

      releaseCtrl();

      ok(ctrlTab.panel.state == "hiding" || ctrlTab.panel.state == "closed",
         "Releasing Ctrl closes the preview panel");
    } else {
      ok(ctrlTab.panel.state == "hiding" || ctrlTab.panel.state == "closed",
         "With " + tabCount + " tabs open, Ctrl+Tab doesn't open the preview panel");
    }

    is(gBrowser.tabContainer.selectedIndex, expectedIndex,
       "With "+ tabCount +" tabs open and tab " + indexStart
       + " selected, Ctrl+Tab*" + tabTimes + " goes " + where);
  }
}