So, here we should, for now, check if DOM localization is completed before firing it.
In the default, pretranslated case, it will be instantly, but in non-pretranslated case (debug build or non-default locale) it will be later.

 We don't have the right check in place yet, but we will very soon. Not sure if worth a comment pointing to bug 1000806 or not.
I'm just writing it to make sure we understand that moz-chrome-dom-loaded will have to be blocked by runtime l10n.