--- a/dom/webbrowserpersist/nsWebBrowserPersist.cpp
+++ b/dom/webbrowserpersist/nsWebBrowserPersist.cpp
@@ -1381,28 +1381,31 @@ nsresult nsWebBrowserPersist::SaveURIInt
             encodedChannel->SetApplyConversion(false);
         }
     }
 
     if (mPersistFlags & PERSIST_FLAGS_FORCE_ALLOW_COOKIES)
     {
         nsCOMPtr<nsIHttpChannelInternal> httpChannelInternal =
                 do_QueryInterface(inputChannel);
-        if (httpChannelInternal)
-            httpChannelInternal->SetThirdPartyFlags(nsIHttpChannelInternal::THIRD_PARTY_FORCE_ALLOW);
+        if (httpChannelInternal) {
+            rv = httpChannelInternal->SetThirdPartyFlags(nsIHttpChannelInternal::THIRD_PARTY_FORCE_ALLOW);
+            MOZ_ASSERT(NS_SUCCEEDED(rv));
+        }
     }
 
     // Set the referrer, post data and headers if any
     nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(inputChannel));
     if (httpChannel)
     {
         // Referrer
         if (aReferrer)
         {
-            httpChannel->SetReferrerWithPolicy(aReferrer, aReferrerPolicy);
+            rv = httpChannel->SetReferrerWithPolicy(aReferrer, aReferrerPolicy);
+            MOZ_ASSERT(NS_SUCCEEDED(rv));
         }
 
         // Post data
         if (aPostData)
         {
             nsCOMPtr<nsISeekableStream> stream(do_QueryInterface(aPostData));
             if (stream)
             {