I don’t feel that the use of UPnP to automatically create port forwarding rules on a router is a good idea.
When you use a router with the NAT enabled and on your LAN is assigned a private subnet (ex. 192.168.0.x), the hosts are automatically protected from malicious access incoming from Internet.
But if the router UPnP aware, enable a port forwarding when a Virus which uses UPnP tells of doing it you expose your LAN to security risks (ex. backdoors).
In any case, if you want to make your ZeroShell firewall UPnP aware, you should install linux-igd package (http://linux-igd.sourceforge.net/).