diff -r 000000000000 -r 6474c204b198 browser/modules/test/browser_taskbar_preview.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/modules/test/browser_taskbar_preview.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,139 @@
+function test() {
+  var isWin7OrHigher = false;
+  try {
+    let version = Cc["@mozilla.org/system-info;1"]
+                    .getService(Ci.nsIPropertyBag2)
+                    .getProperty("version");
+    isWin7OrHigher = (parseFloat(version) >= 6.1);
+  } catch (ex) { }
+
+  is(!!Win7Features, isWin7OrHigher, "Win7Features available when it should be");
+  if (!isWin7OrHigher)
+    return;
+
+  const ENABLE_PREF_NAME = "browser.taskbar.previews.enable";
+
+  let temp = {};
+  Cu.import("resource:///modules/WindowsPreviewPerTab.jsm", temp);
+  let AeroPeek = temp.AeroPeek;
+
+  waitForExplicitFinish();
+
+  gPrefService.setBoolPref(ENABLE_PREF_NAME, true);
+
+  is(1, AeroPeek.windows.length, "Got the expected number of windows");
+
+  checkPreviews(1, "Browser starts with one preview");
+
+  gBrowser.addTab();
+  gBrowser.addTab();
+  gBrowser.addTab();
+
+  checkPreviews(4, "Correct number of previews after adding");
+
+  for each (let preview in AeroPeek.previews)
+    ok(preview.visible, "Preview is shown as expected");
+
+  gPrefService.setBoolPref(ENABLE_PREF_NAME, false);
+  checkPreviews(4, "Previews are unchanged when disabling");
+
+  for each (let preview in AeroPeek.previews)
+    ok(!preview.visible, "Preview is not shown as expected after disabling");
+
+  gPrefService.setBoolPref(ENABLE_PREF_NAME, true);
+  checkPreviews(4, "Previews are unchanged when re-enabling");
+  for each (let preview in AeroPeek.previews)
+    ok(preview.visible, "Preview is shown as expected after re-enabling");
+
+  [1,2,3,4].forEach(function (idx) {
+    gBrowser.selectedTab = gBrowser.tabs[idx];
+    ok(checkSelectedTab(), "Current tab is correctly selected");
+  });
+
+  let currentSelectedTab = gBrowser.selectedTab;
+  for each (let idx in [1,2,3,4]) {
+    let preview = getPreviewForTab(gBrowser.tabs[0]);
+    let canvas = createThumbnailSurface(preview);
+    let ctx = canvas.getContext("2d");
+    preview.controller.drawThumbnail(ctx, canvas.width, canvas.height);
+    ok(currentSelectedTab.selected, "Drawing thumbnail does not change selection");
+    canvas = getCanvas(preview.controller.width, preview.controller.height);
+    ctx = canvas.getContext("2d");
+    preview.controller.drawPreview(ctx);
+    ok(currentSelectedTab.selected, "Drawing preview does not change selection");
+  }
+
+  // Close #4
+  getPreviewForTab(gBrowser.selectedTab).controller.onClose();
+  checkPreviews(3, "Expected number of previews after closing selected tab via controller");
+  ok(gBrowser.tabs.length == 3, "Successfully closed a tab");
+
+  // Select #1
+  ok(getPreviewForTab(gBrowser.tabs[0]).controller.onActivate(), "Activation was accepted");
+  ok(gBrowser.tabs[0].selected, "Correct tab was selected");
+  checkSelectedTab();
+
+  // Remove #3 (non active)
+  gBrowser.removeTab(gBrowser.tabContainer.lastChild);
+  checkPreviews(2, "Expected number of previews after closing unselected via browser");
+
+  // Remove #1 (active)
+  gBrowser.removeTab(gBrowser.tabContainer.firstChild);
+  checkPreviews(1, "Expected number of previews after closing selected tab via browser");
+
+  // Add a new tab
+  gBrowser.addTab();
+  checkPreviews(2);
+  // Check default selection
+  checkSelectedTab();
+
+  // Change selection
+  gBrowser.selectedTab = gBrowser.tabs[0];
+  checkSelectedTab();
+  // Close nonselected tab via controller
+  getPreviewForTab(gBrowser.tabs[1]).controller.onClose();
+  checkPreviews(1);
+
+  if (gPrefService.prefHasUserValue(ENABLE_PREF_NAME))
+    gPrefService.clearUserPref(ENABLE_PREF_NAME);
+
+  finish();
+
+  function checkPreviews(aPreviews, msg) {
+    let nPreviews = AeroPeek.previews.length;
+    is(aPreviews, gBrowser.tabs.length, "Browser has expected number of tabs");
+    is(nPreviews, gBrowser.tabs.length, "Browser has one preview per tab");
+    is(nPreviews, aPreviews, msg || "Got expected number of previews");
+  }
+
+  function getPreviewForTab(tab)
+    window.gTaskbarTabGroup.previewFromTab(tab);
+
+  function checkSelectedTab()
+    getPreviewForTab(gBrowser.selectedTab).active;
+
+  function isTabSelected(idx)
+    gBrowser.tabs[idx].selected;
+
+  function createThumbnailSurface(p) {
+    let thumbnailWidth = 200,
+        thumbnailHeight = 120;
+    let ratio = p.controller.thumbnailAspectRatio;
+
+    if (thumbnailWidth/thumbnailHeight > ratio)
+      thumbnailWidth = thumbnailHeight * ratio;
+    else
+      thumbnailHeight = thumbnailWidth / ratio;
+
+    return getCanvas(thumbnailWidth, thumbnailHeight);
+  }
+
+  function getCanvas(width, height) {
+    let win = window.QueryInterface(Ci.nsIDOMWindow);
+    let doc = win.document;
+    let canvas = doc.createElementNS("http://www.w3.org/1999/xhtml", "canvas");
+    canvas.width = width;
+    canvas.height = height;
+    return canvas;
+  }
+}