diff -r 000000000000 -r 6474c204b198 browser/metro/base/tests/mochitest/browser_prompt.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/metro/base/tests/mochitest/browser_prompt.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,39 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+function test() {
+  waitForExplicitFinish();
+  runTests();
+}
+
+gTests.push({
+  desc: "Test getPrompt with null domWindow (bug 949333)",
+  run: function () {
+    let factory = Cc["@mozilla.org/prompter;1"].getService(Ci.nsIPromptFactory);
+    let prompter = factory.getPrompt(null, Ci.nsIPrompt);
+
+    let browser = getBrowser();
+    let dialogOpened = false;
+
+    Task.spawn(function() {
+      yield waitForEvent(browser, "DOMWillOpenModalDialog");
+      dialogOpened = true;
+
+      yield waitForMs(0);
+      let stack = browser.parentNode;
+      let dialogs = stack.getElementsByTagNameNS(XUL_NS, "tabmodalprompt");
+      is(dialogs.length, 1, "one tab-modal dialog showing");
+
+      let dialog = dialogs[0];
+      let okButton = dialog.ui.button0;
+      okButton.click();
+    });
+
+    prompter.alert("Test", "test");
+
+    ok(dialogOpened, "Dialog was opened");
+  }
+});