diff -r 000000000000 -r 6474c204b198 browser/base/content/test/general/browser_visibleTabs_tabPreview.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/base/content/test/general/browser_visibleTabs_tabPreview.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,41 @@
+/* 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/. */
+
+function test() {
+  gPrefService.setBoolPref("browser.ctrlTab.previews", true);
+
+  let [origTab] = gBrowser.visibleTabs;
+  let tabOne = gBrowser.addTab();
+  let tabTwo = gBrowser.addTab();
+
+  // test the ctrlTab.tabList
+  pressCtrlTab();
+  ok(ctrlTab.tabList.length, 3, "Show 3 tabs in tab preview");
+  releaseCtrl();
+
+  gBrowser.showOnlyTheseTabs([origTab]);
+  pressCtrlTab();
+  ok(ctrlTab.tabList.length, 1, "Show 1 tab in tab preview");
+  ok(!ctrlTab.isOpen, "With 1 tab open, Ctrl+Tab doesn't open the preview panel");
+
+  gBrowser.showOnlyTheseTabs([origTab, tabOne, tabTwo]);
+  pressCtrlTab();
+  ok(ctrlTab.isOpen, "With 3 tabs open, Ctrl+Tab does open the preview panel");
+  releaseCtrl();
+
+  // cleanup
+  gBrowser.removeTab(tabOne);
+  gBrowser.removeTab(tabTwo);
+
+  if (gPrefService.prefHasUserValue("browser.ctrlTab.previews"))
+    gPrefService.clearUserPref("browser.ctrlTab.previews");
+}
+
+function pressCtrlTab(aShiftKey) {
+  EventUtils.synthesizeKey("VK_TAB", { ctrlKey: true, shiftKey: !!aShiftKey });
+}
+
+function releaseCtrl() {
+  EventUtils.synthesizeKey("VK_CONTROL", { type: "keyup" });
+}