I’m seeing the same thing. It actually is logging me in — I can get to the admin area by clicking an edit link on a post — just not through the login page. At first glance, it seems like maybe FF is caching the wp-admin to wp-login.php redirect and replaying it but clearing the cache and cookies didn’t help.
If I click logout in the admin screen, the login will work the next time, but then it goes back to the same behavior the next time I try to log in.
IE works fine.
using FF 3.0.7 on Vista
