diff -r 000000000000 -r 6474c204b198 layout/base/crashtests/401589-1.xul
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/base/crashtests/401589-1.xul	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,29 @@
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        xmlns:html="http://www.w3.org/1999/xhtml"
+        xmlns:math="http://www.w3.org/1998/Math/MathML"
+        class="reftest-wait"
+        onload="boom();">
+        
+<html:style type="text/css">
+[class="mp"] { display: -moz-popup; }
+</html:style>
+
+<script>
+
+function boom()
+{
+  document.getElementById("mtd").setAttribute("class", "mp");
+  setTimeout(boom2, 30);
+}
+
+function boom2()
+{
+  document.getElementById("mtd").setAttribute("class", "");
+  document.documentElement.removeAttribute("class");
+}
+
+</script>
+
+<math:mtd id="mtd" />
+
+</window>