--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -947,34 +947,34 @@ void Navigator::CheckProtocolHandlerAllo
   nsCOMPtr<nsIProtocolHandler> handler;
   nsCOMPtr<nsIIOService> io = services::GetIOService();
   if (NS_FAILED(
           io->GetProtocolHandler(scheme.get(), getter_AddRefs(handler)))) {
     raisePermissionDeniedScheme();
     return;
   }
 
-  // Check to make sure this isn't already handled internally (we don't
-  // want to let them take over, say "chrome"). In theory, the checks above
-  // should have already taken care of this.
-  nsCOMPtr<nsIExternalProtocolHandler> externalHandler =
-      do_QueryInterface(handler);
-  MOZ_RELEASE_ASSERT(
-      externalHandler,
-      "We should never allow overriding a builtin protocol handler");
-
   // check if we have prefs set saying not to add this.
   bool defaultExternal =
       Preferences::GetBool("network.protocol-handler.external-default");
   nsPrintfCString specificPref("network.protocol-handler.external.%s",
                                scheme.get());
   if (!Preferences::GetBool(specificPref.get(), defaultExternal)) {
     raisePermissionDeniedScheme();
     return;
   }
+
+  // Check to make sure this isn't already handled internally (we don't
+  // want to let them take over, say "chrome"). In theory, the checks above
+  // should have already taken care of this.
+  nsCOMPtr<nsIExternalProtocolHandler> externalHandler =
+      do_QueryInterface(handler);
+  MOZ_RELEASE_ASSERT(
+      externalHandler,
+      "We should never allow overriding a builtin protocol handler");
 }
 
 void Navigator::RegisterProtocolHandler(const nsAString& aScheme,
                                         const nsAString& aURI,
                                         const nsAString& aTitle,
                                         ErrorResult& aRv) {
   if (!mWindow || !mWindow->GetOuterWindow() || !mWindow->GetDocShell() ||
       !mWindow->GetDoc()) {