diff --git a/ipc/mscom/EnsureMTA.cpp b/ipc/mscom/EnsureMTA.cpp
old mode 100644
new mode 100755
index 0c543fd88ab2..c4b27fb801fb
--- a/ipc/mscom/EnsureMTA.cpp
+++ b/ipc/mscom/EnsureMTA.cpp
@@ -33,7 +33,7 @@ public:
   BackgroundMTAData()
   {
     nsCOMPtr<nsIRunnable> runnable = new EnterMTARunnable();
-    nsresult rv = NS_NewNamedThread("COM MTA",
+    mozilla::DebugOnly<nsresult> rv = NS_NewNamedThread("COM MTA",
                                     getter_AddRefs(mThread), runnable);
     NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "NS_NewNamedThread failed");
     MOZ_ASSERT(NS_SUCCEEDED(rv));