I get the same problem. It worked at first, but suddenly decided it didn't want to work anymore and quit out. I highly doubt it has anything to do with a firewall. I can just do what was suggested and copy down IPs and join manually, but that crap takes forever, so i'd like to try to find a way to fix it.
If it helps at all, it stopped working right after i got vote-kicked from the Beer Garden server. It was my first real time playing, and i was on the human team. I played for a bit, then after a while I got frustrated that i couldn't build more turrets because i lacked enough power, despite the fact that i was away from my base and standing next to a repeater. Anyway, i quit the server and rejoined on the alien side, since i saw no way change teams in-game, and was immediatly vote-kicked by the jerks in the server, probably for team swapping, even though it was a 3 on 4 game, and i was the extra member. That's when it stopped working.
When i try to get a server list, it gives me the message "Rrfreshing/getting info/blahblah whatever for -1 servers" and just sits there.
