--- a/dom/src/base/nsDOMClassInfo.cpp
+++ b/dom/src/base/nsDOMClassInfo.cpp
@@ -4505,20 +4505,24 @@ nsWindowSH::GetProperty(nsIXPConnectWrap
     //
     // Calling GetWrappedNativeOfJSObject() is not all that cheap, so
     // only do that if the JSClass name is one that is likely to be a
     // window object.
 
     const char *name = JS_GET_CLASS(cx, JSVAL_TO_OBJECT(*vp))->name;
 
     // The list of Window class names here need to be kept in sync
-    // with the actual class names!
+    // with the actual class names! The class name
+    // XPCCrossOriginWrapper needs to be handled here too as XOWs
+    // define child frame names with a XOW as the value, and thus
+    // we'll need to get through here with XOWs class name too.
     if ((*name == 'W' && strcmp(name, "Window") == 0) ||
         (*name == 'C' && strcmp(name, "ChromeWindow") == 0) ||
-        (*name == 'M' && strcmp(name, "ModalContentWindow") == 0)) {
+        (*name == 'M' && strcmp(name, "ModalContentWindow") == 0) ||
+        (*name == 'X' && strcmp(name, "XPCCrossOriginWrapper") == 0)) {
       nsCOMPtr<nsIXPConnectWrappedNative> vpwrapper;
       sXPConnect->GetWrappedNativeOfJSObject(cx, JSVAL_TO_OBJECT(*vp),
                                              getter_AddRefs(vpwrapper));
 
       if (vpwrapper) {
         nsCOMPtr<nsIDOMWindow> window(do_QueryWrappedNative(vpwrapper));
 
         if (window) {

--- a/dom/tests/mochitest/bugs/Makefile.in
+++ b/dom/tests/mochitest/bugs/Makefile.in
@@ -72,12 +72,14 @@ include $(topsrcdir)/config/rules.mk
 		iframe_bug424093.html \
 		test_bug409349.html \
 		iframe_bug409349.html \
 		test_bug411103.html \
 		test_bug414291.html \
 		test_bug430276.html \
 		iframe_bug430276.html \
 		iframe_bug430276-2.html \
+		test_bug440572.html \
+		iframe_bug440572.html \
 		$(NULL)
 
 libs:: 	$(_TEST_FILES)
 	$(INSTALL) $(foreach f,$^,"$f") $(DEPTH)/_tests/testing/mochitest/tests/$(relativesrcdir)