add_task(async function test() {
  const kTestURI =
    "data:text/html," +
    "<script type=\"text/javascript\">" +
    "  function onMouseDown(aEvent) {" +
    "    document.getElementById('willBeFocused').focus();" +
    "    aEvent.preventDefault();" +
    "  }" +
    "</script>" +
    "<body id=\"body\">" +
    "<button onmousedown=\"onMouseDown(event);\" style=\"width: 100px; height: 100px;\">click here</button>" +
    "<input id=\"willBeFocused\"></body>";

  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, kTestURI);

  let fm = Cc["@mozilla.org/focus-manager;1"].
        getService(Ci.nsIFocusManager);

  for (var button = 0; button < 3; button++) {
    // Set focus to a chrome element before synthesizing a mouse down event.
    document.getElementById("urlbar").focus();

    is(fm.focusedElement, document.getElementById("urlbar").inputField,
       "Failed to move focus to search bar: button=" + button);

    // Synthesize mouse down event on browser object over the button, such that
    // the event propagates through both processes.
    EventUtils.synthesizeMouse(tab.linkedBrowser, 20, 20, { "button": button }, null);

    isnot(fm.focusedElement, document.getElementById("urlbar").inputField,
       "Failed to move focus away from search bar: button=" + button);

    await ContentTask.spawn(tab.linkedBrowser, button, async function (button) {
      let fm = Cc["@mozilla.org/focus-manager;1"].
          getService(Ci.nsIFocusManager);

      let attempts = 10;
      await new Promise(resolve => {
        function check() {
          if (attempts > 0 && content.document.activeElement.id != "willBeFocused") {
            attempts--;
            content.window.setTimeout(check, 100);
            return;
          }

          Assert.equal(content.document.activeElement.id, "willBeFocused",
                       "The input element isn't active element: button=" + button);
          Assert.equal(fm.focusedElement, content.document.activeElement,
                       "The active element isn't focused element in App level: button=" + button);
          resolve();
        }
        check();
      });
    });
  }

  gBrowser.removeTab(tab);
});
