--- a/dom/xbl/nsXBLPrototypeHandler.cpp
+++ b/dom/xbl/nsXBLPrototypeHandler.cpp
@@ -732,16 +732,17 @@ nsXBLPrototypeHandler::ConstructPrototyp
                                           const char16_t* aGroup,
                                           const char16_t* aPreventDefault,
                                           const char16_t* aAllowUntrusted)
 {
   mType = 0;
 
   if (aKeyElement) {
     mType |= NS_HANDLER_TYPE_XUL;
+    MOZ_ASSERT(!mPrototypeBinding);
     nsCOMPtr<nsIWeakReference> weak = do_GetWeakReference(aKeyElement);
     if (!weak) {
       return;
     }
     weak.swap(mHandlerElement);
   }
   else {
     mType |= aCommand ? NS_HANDLER_TYPE_XBL_COMMAND : NS_HANDLER_TYPE_XBL_JS;
@@ -831,22 +832,24 @@ nsXBLPrototypeHandler::ConstructPrototyp
     if (mKeyMask == 0)
       mKeyMask = cAllModifiers;
     ToLowerCase(key);
 
     // We have a charcode.
     mMisc = 1;
     mDetail = key[0];
     const uint8_t GTK2Modifiers = cShift | cControl | cShiftMask | cControlMask;
-    if ((mKeyMask & GTK2Modifiers) == GTK2Modifiers &&
+    if ((mType & NS_HANDLER_TYPE_XUL) &&
+        (mKeyMask & GTK2Modifiers) == GTK2Modifiers &&
         modifiers.First() != char16_t(',') &&
         (mDetail == 'u' || mDetail == 'U'))
       ReportKeyConflict(key.get(), modifiers.get(), aKeyElement, "GTK2Conflict2");
     const uint8_t WinModifiers = cControl | cAlt | cControlMask | cAltMask;
-    if ((mKeyMask & WinModifiers) == WinModifiers &&
+    if ((mType & NS_HANDLER_TYPE_XUL) &&
+        (mKeyMask & WinModifiers) == WinModifiers &&
         modifiers.First() != char16_t(',') &&
         (('A' <= mDetail && mDetail <= 'Z') ||
          ('a' <= mDetail && mDetail <= 'z')))
       ReportKeyConflict(key.get(), modifiers.get(), aKeyElement, "WinConflict2");
   }
   else {
     key.Assign(aKeyCode);
     if (mType & NS_HANDLER_TYPE_XUL)
@@ -880,17 +883,17 @@ void
 nsXBLPrototypeHandler::ReportKeyConflict(const char16_t* aKey, const char16_t* aModifiers, nsIContent* aKeyElement, const char *aMessageName)
 {
   nsCOMPtr<nsIDocument> doc;
   if (mPrototypeBinding) {
     nsXBLDocumentInfo* docInfo = mPrototypeBinding->XBLDocumentInfo();
     if (docInfo) {
       doc = docInfo->GetDocument();
     }
-  } else if (aKeyElement) {
+  } else {
     doc = aKeyElement->OwnerDoc();
   }
 
   nsAutoString id;
   aKeyElement->GetAttr(kNameSpaceID_None, nsGkAtoms::id, id);
   const char16_t* params[] = { aKey, aModifiers, id.get() };
   nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
                                   NS_LITERAL_CSTRING("XBL Prototype Handler"), doc,