diff -r 000000000000 -r 6474c204b198 toolkit/components/thumbnails/test/browser_thumbnails_bg_no_alert.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_bg_no_alert.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,13 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function runTests() {
+  let url = "data:text/html,<script>try { alert('yo!'); } catch (e) {}</script>";
+  ok(!thumbnailExists(url), "Thumbnail file should not already exist.");
+
+  let capturedURL = yield bgCapture(url);
+  is(capturedURL, url, "Captured URL should be URL passed to capture.");
+  ok(thumbnailExists(url),
+     "Thumbnail file should exist even though it alerted.");
+  removeThumbnail(url);
+}