It would have to use a port that your firewall can proxy. Since port 80 is used for HTTP (web surfing) you might try searching for chat scripts that use it (all firewalls proxy port 80).
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.