gecko-dev/editor/libeditor/tests/browser_bug527935.js

add_task(async function() {
  await new Promise(resolve => waitForFocus(resolve, window));

  const kPageURL =
    "http://example.org/browser/editor/libeditor/tests/bug527935.html";
  await BrowserTestUtils.withNewTab(
    {
      gBrowser,
      url: kPageURL,
    },
    async function(aBrowser) {
      var popupShown = false;
      function listener() {
        popupShown = true;
      }
      SpecialPowers.addAutoCompletePopupEventListener(
        window,
        "popupshowing",
        listener
      );

      await ContentTask.spawn(aBrowser, {}, async function() {
        var window = content.window.wrappedJSObject;
        var document = window.document;
        var formTarget = document.getElementById("formTarget");
        var initValue = document.getElementById("initValue");

        window.loadPromise = new Promise(resolve => {
          formTarget.onload = resolve;
        });

        initValue.focus();
        initValue.value = "foo";
      });

      EventUtils.synthesizeKey("KEY_Enter");

      await ContentTask.spawn(aBrowser, {}, async function() {
        var window = content.window.wrappedJSObject;
        var document = window.document;

        await window.loadPromise;

        var newInput = document.createElement("input");
        newInput.setAttribute("name", "test");
        document.body.appendChild(newInput);

        var event = document.createEvent("KeyboardEvent");

        event.initKeyEvent(
          "keypress",
          true,
          true,
          null,
          false,
          false,
          false,
          false,
          0,
          "f".charCodeAt(0)
        );
        newInput.value = "";
        newInput.focus();
        newInput.dispatchEvent(event);
      });

      await new Promise(resolve => hitEventLoop(resolve, 100));

      ok(!popupShown, "Popup must not be opened");
      SpecialPowers.removeAutoCompletePopupEventListener(
        window,
        "popupshowing",
        listener
      );
    }
  );
});

function hitEventLoop(func, times) {
  if (times > 0) {
    setTimeout(hitEventLoop, 0, func, times - 1);
  } else {
    setTimeout(func, 0);
  }
}