diff -r 000000000000 -r 6474c204b198 toolkit/components/thumbnails/test/browser_thumbnails_bg_no_cookies_sent.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_bg_no_cookies_sent.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,38 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function runTests() {
+  // Visit the test page in the browser and tell it to set a cookie.
+  let url = bgTestPageURL({ setGreenCookie: true });
+  let tab = gBrowser.loadOneTab(url, { inBackground: false });
+  let browser = tab.linkedBrowser;
+  yield whenLoaded(browser);
+
+  // The root element of the page shouldn't be green yet.
+  let greenStr = "rgb(0, 255, 0)";
+  isnot(browser.contentDocument.documentElement.style.backgroundColor,
+        greenStr,
+        "The page shouldn't be green yet.");
+
+  // Cookie should be set now.  Reload the page to verify.  Its root element
+  // will be green if the cookie's set.
+  browser.reload();
+  yield whenLoaded(browser);
+  is(browser.contentDocument.documentElement.style.backgroundColor,
+     greenStr,
+     "The page should be green now.");
+
+  // Capture the page.  Get the image data of the capture and verify it's not
+  // green.  (Checking only the first pixel suffices.)
+  yield bgCapture(url);
+  ok(thumbnailExists(url), "Thumbnail file should exist after capture.");
+
+  retrieveImageDataForURL(url, function ([r, g, b]) {
+    isnot([r, g, b].toString(), [0, 255, 0].toString(),
+          "The captured page should not be green.");
+    gBrowser.removeTab(tab);
+    removeThumbnail(url);
+    next();
+  });
+  yield true;
+}