Cookies expire at end of browser session?

So using Firefox 12.0, I look at the cookies MP places when I log in, and the user cookie...actually all the cookies, have an expiration at the end of the session.

This is a giant PITA, in that everytime I've closed a browser and later return to MP, I have to log in again. FF also doesn't recognize that the login java popup or whatever it is, is something it should prompt to remember a password/username for.

What am I missing here?

Are these user cookies really supposed to be set with an expiration at the end of the session?

This is specific to FF12 apparently, as the cookies behave fine in other browsers. I suspect a bug in FF12.