diff --git a/content/base/public/nsContentUtils.h b/content/base/public/nsContentUtils.h
index 1ba2a603e50a..c0ce356f291d 100644
--- a/content/base/public/nsContentUtils.h
+++ b/content/base/public/nsContentUtils.h
@@ -1411,6 +1411,12 @@ public:
   static already_AddRefed<nsIDocument>
   GetDocumentFromScriptContext(nsIScriptContext *aScriptContext);
 
+  /**
+   * The method checks whether the caller can access native anonymous content.
+   * If there is no JS in the stack or privileged JS is running, this
+   * method returns PR_TRUE, otherwise PR_FALSE.
+   */
+  static PRBool CanAccessNativeAnon();
 private:
 
   static PRBool InitializeEventTable();
diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index c4b035915063..0bc447356c67 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -176,6 +176,7 @@ static NS_DEFINE_CID(kXTFServiceCID, NS_XTFSERVICE_CID);
 #include "nsIConsoleService.h"
 
 #include "mozAutoDocUpdate.h"
+#include "jsinterp.h"
 
 const char kLoadAsData[] = "loadAsData";
 
@@ -4943,3 +4944,55 @@ nsContentTypeParser::GetParameter(const char* aParameterName, nsAString& aResult
                                 EmptyCString(), PR_FALSE, nsnull,
                                 aResult);
 }
+
+/* static */
+
+// If you change this code, change also AllowedToAct() in
+// XPCSystemOnlyWrapper.cpp!
+PRBool
+nsContentUtils::CanAccessNativeAnon()
+{
+  JSContext* cx = nsnull;
+  sThreadJSContextStack->Peek(&cx);
+  if (!cx) {
+    return PR_TRUE;
+  }
+  JSStackFrame* fp;
+  nsIPrincipal* principal =
+    sSecurityManager->GetCxSubjectPrincipalAndFrame(cx, &fp);
+  NS_ENSURE_TRUE(principal, PR_FALSE);
+
+  if (!fp) {
+    if (!JS_FrameIterator(cx, &fp)) {
+      // No code at all is running. So we must be arriving here as the result
+      // of C++ code asking us to do something. Allow access.
+      return PR_TRUE;
+    }
+
+    // Some code is running, we can't make the assumption, as above, but we
+    // can't use a native frame, so clear fp.
+    fp = nsnull;
+  }
+
+  void *annotation = fp ? JS_GetFrameAnnotation(cx, fp) : nsnull;
+  PRBool privileged;
+  if (NS_SUCCEEDED(principal->IsCapabilityEnabled("UniversalXPConnect",
+                                                  annotation,
+                                                  &privileged)) &&
+      privileged) {
+    // UniversalXPConnect things are allowed to touch us.
+    return PR_TRUE;
+  }
+
+  // XXX HACK EWW! Allow chrome://global/ access to these things, even
+  // if they've been cloned into less privileged contexts.
+  static const char prefix[] = "chrome://global/";
+  const char *filename;
+  if (fp && fp->script &&
+      (filename = fp->script->filename) &&
+      !strncmp(filename, prefix, NS_ARRAY_LENGTH(prefix) - 1)) {
+    return PR_TRUE;
+  }
+
+  return PR_FALSE;
+}
diff --git a/content/events/src/nsDOMMouseEvent.cpp b/content/events/src/nsDOMMouseEvent.cpp
index 8b321671d907..d6234ee1421f 100644
--- a/content/events/src/nsDOMMouseEvent.cpp
+++ b/content/events/src/nsDOMMouseEvent.cpp
@@ -196,6 +196,15 @@ nsDOMMouseEvent::GetRelatedTarget(nsIDOMEventTarget** aRelatedTarget)
   }
 
   if (relatedTarget) {
+    nsCOMPtr<nsIContent> content = do_QueryInterface(relatedTarget);
+    if (content && content->IsInNativeAnonymousSubtree() &&
+        !nsContentUtils::CanAccessNativeAnon()) {
+      relatedTarget = content->FindFirstNonNativeAnonymous();
+      if (!relatedTarget) {
+        return NS_OK;
+      }
+    }
+
     CallQueryInterface(relatedTarget, aRelatedTarget);
   }
   return NS_OK;
diff --git a/js/src/xpconnect/src/XPCSystemOnlyWrapper.cpp b/js/src/xpconnect/src/XPCSystemOnlyWrapper.cpp
index 6fe00ead76b8..0d69f70b61d3 100644
--- a/js/src/xpconnect/src/XPCSystemOnlyWrapper.cpp
+++ b/js/src/xpconnect/src/XPCSystemOnlyWrapper.cpp
@@ -160,6 +160,7 @@ GetWrappedObject(JSContext *cx, JSObject *wrapper)
   return XPCWrapper::UnwrapGeneric(cx, &sXPC_SOW_JSClass, wrapper);
 }
 
+// If you change this code, change also nsContentUtils::CanAccessNativeAnon()!
 JSBool
 AllowedToAct(JSContext *cx, jsval idval)
 {