tried a few, no problems there. i would just say, back up your important stuff and reinstall snow leopard. something silly is wrong, and it'll take way more of your time trying to figure it out than to just start fresh. i would back up using carbon copy cloner, so that you can see exactly what you had before.
fyi, the firewall i use it called 'WaterRoof'... it's kind of a lower-level firewall, not very GUI but good for what i use it for.