Bug 590883. Don't forget to null-check the viewer, since the external resource load might have failed. r=roc a=blocking

content/base/src/nsDocument.cpp

@@ -845,7 +845,9 @@ ExternalResourceShower(nsIURI* aKey,
                        nsExternalResourceMap::ExternalResource* aData,
                        void* aClosure)
 {
+  if (aData->mViewer) {
     aData->mViewer->Show();
+  }
   return PL_DHASH_NEXT;
 }