I'm on Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 4.0.20506) too (Vista instead of XP and english) and I haven't got any problem, logging in does take you to the form though? you just go to the challenges and your still logged in (if you have cookies on I guess) so you can do the challenges?
my guess would be that you are typing in the wrong password/firefox is remembering an old one, are you relying on your current browser remembering your session/password so you don't have to login again? have you tried the username and password on another computer or browser?
you could make the post if IE had stayed logged in from prior to some password change or you could be logging in with remembered form details (so some username+password combo is saved) in which case you can only assume what password your logged in with (maybe you got outrageously drunk and changed your password then forgot you did so). As it appears to be down to the browser the best guess I can come up with is that your firefox has crashed (or been terminated) which has caused it to mess up its database or something along those lines (this is why I guess that) so the simplest solution would be to export all of your bookmarks and then reinstall firefox (you could try the 'fix' option of the installer if it has one first).
If you google around some more you might find a better solution that will repair the database or whatever the problem is which could save your history and saved forms data, I'm not familiar with FF bugs as I'm on a well behaved system (aside from graphics but thats a different story) so I can't be of more help at the moment
I concur - it is getting ridiculous now, from a quick glance the accounts responsible are less than a month old so would have been created after the ''complete a level of any game" captcha came into effect (so I think, unless this is a recent as in less than a week old addition), so this would suggest that captchas are futile as they get solved by a human operator anyway in which case it might require a more hands on approach to stop this scourge such as moderators yakyakyakyak for the time being until further measures are installed. I think creating a content/user filter could do the trick for the most part but I've said this all before somewhere, still I'd be happy to contribute as it looks like I have a quite couple of weeks coming up.
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