Login problem with 1.5.1.3

My apologies if somebody has brought this up before — I can’t imagine nobody has, but I couldn’t find any information. I upgraded from plain 1.5 to 1.5.1.3 the other day, and ever since, I can’t log in. I can get into the control panel with IE, which remembers that I’m logged in (so I just click on Edit Post to get in), but Firefox doesn’t remember me, so I’m out of luck.

In either IE or Firefox, when I click on my login link, the browser hangs and hangs and hangs some more and eventually just stops trying. I even tried going back to the original 1.5 version of wp-login.php, but no dice.

Any ideas? Anybody else experience this? For what it’s worth, I’m not 100-percent sure this problem has to do with my upgrade, but the two events seemed to happen at the same time.