Dunno if this is a real bug or a design decision (nor if it was already reported, couldnt find a dupe) but the 'do you want to save passwd?' popup doesnt show the fqdn of the requesting website. Ie if i visit www.foo.com, or dev,foo.com or prod.foo.com it will only show 'foo.com' in the popup, while this can be three different websites. The saved passwd is correctly associated with the fqdn in the passwd manager though. Dunno what happens too for www.foo.com/bar and www.foo.com/quux, which could also be two different auths. They only show foo.com in the popup, so this might be misleading. Checked with 14.0.1 and trunk.

I don't know the password manager code that well but it seems that it is saving the hostname and not only the domain. Is the doorhanger only prompting the domain for some reasons?

This is intentional, from bug 403420. The fqdn is stored internally, but the displayed string is kept short. Helps prevent overly-wordy prompts.

[reopening, to make sure the comment is seen] I wonder if only showing the domain instead of the host can't be misleading and provides security risks. If we really care about saving space, can't we simply remove the website name? Given that we are using a doorhanger, it seems like the user is having enough context and we wouldn't provide potentially misleading information to the user.

Fixed by bug 1175300 + bug 1144856