Gnutella works through a firewall via "push", if you need to kick start your client, try entering some IPs from a list at clip2.com

If you can browse through your firewall you can use gnutella, it's that simple. Gnutella uses the same system as your browser, and NO your browser doesn't use port 80! Web SERVERS use port 80 and you should have that blocked unless you are running a web server, which sort of defeats the security reason you have a firewall.

Point being, a firewall will allow you to CREATE any connections you need. It just doesn't allow someone else to connect from outside.

REPEATE: Firewalls allow two way communication but YOU HAVE TO START/ORIGINATE THE CONNECTION. Is that clear yet?

So if you don't understand why Gnutella works on a firewall, please read above again.

Oh, by now you should also understand that push is only need for someone to get a file from you, you make a connection to get a file from someone else so a firewall is not a problem.