--- a/mailnews/base/src/nsMessengerBootstrap.cpp
+++ b/mailnews/base/src/nsMessengerBootstrap.cpp
@@ -291,17 +291,17 @@ NS_IMETHODIMP nsMessengerBootstrap::Open
   // create scriptable versions of our strings that we can store in our nsISupportsArray....
   if (aFolderURI)
   {
     if (standAloneMsgWindow)
     {
       nsCOMPtr <nsIMsgFolder> folder;
       rv = GetExistingFolder(nsDependentCString(aFolderURI), getter_AddRefs(folder));
       NS_ENSURE_SUCCESS(rv, rv);
-      nsXPIDLCString msgUri;
+      nsCAutoString msgUri;
       folder->GetBaseMessageURI(msgUri);
 
       nsCOMPtr<nsISupportsCString> scriptableMsgURI (do_CreateInstance(NS_SUPPORTS_CSTRING_CONTRACTID));
       NS_ENSURE_TRUE(scriptableMsgURI, NS_ERROR_FAILURE);
       msgUri.Append('#');
       msgUri.AppendInt(aMessageKey, 10);
       scriptableMsgURI->SetData(msgUri);
       argsArray->AppendElement(scriptableMsgURI);