Have a look at the following screen:
This is the screen Firefox shows me when a site requires me to log in. Note that there is no information about the URL of the site or the realm requesting me to log in. You can imagine the problem this gives when I open many tabs at the same time: I have no idea of which site is going to receive my details.
This problem only occurs in the Spanish version of Firefox; I also installed the English version, which showed me the necessary information.
