--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -166,34 +166,46 @@ private:
             NS_WARNING("Failed to dispatch to stream transport service!");
 
             // It's probably safer to take the main thread IO hit here rather
             // than leak a file descriptor.
             CloseFile();
         }
     }
 
-    void OpenFile()
+    // Helper method to avoid gnarly control flow for failures.
+    void OpenFileImpl()
     {
         MOZ_ASSERT(!NS_IsMainThread());
         MOZ_ASSERT(!mFD);
 
         nsCOMPtr<nsIFile> file;
         nsresult rv = NS_NewLocalFile(mPath, false, getter_AddRefs(file));
         NS_ENSURE_SUCCESS_VOID(rv);
 
         PRFileDesc* fd;
         rv = file->OpenNSPRFileDesc(PR_RDONLY, 0, &fd);
         NS_ENSURE_SUCCESS_VOID(rv);
 
         mFD = fd;
+    }
+
+    void OpenFile()
+    {
+        MOZ_ASSERT(!NS_IsMainThread());
+
+        OpenFileImpl();
 
         if (NS_FAILED(NS_DispatchToMainThread(this))) {
             NS_WARNING("Failed to dispatch to main thread!");
 
+            // Intentionally leak the runnable (but not the fd) rather
+            // than crash when trying to release a main thread object
+            // off the main thread.
+            mTabParent.forget();
             CloseFile();
         }
     }
 
     void CloseFile()
     {
         // It's possible for this to happen on the main thread if the dispatch
         // to the stream service fails after we've already opened the file so