diff -r 000000000000 -r 6474c204b198 testing/mochitest/tests/SimpleTest/iframe-between-tests.html
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/testing/mochitest/tests/SimpleTest/iframe-between-tests.html	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,17 @@
+<title>iframe for between tests</title>
+<!--
+  This page exists so that our accounting for assertions correctly
+  counts assertions that happen while leaving a page.  We load this page
+  after a test finishes, check the assertion counts, and then go on to
+  load the next.
+-->
+<script>
+window.addEventListener("load", function() {
+  var runner = (parent.TestRunner || parent.wrappedJSObject.TestRunner);
+  runner.testUnloaded();
+
+  if (SpecialPowers) {
+    SpecialPowers.DOMWindowUtils.runNextCollectorTimer();
+  }
+});
+</script>