I didn't have any problems with my IPFW setup upon upgrading to Panther. I'm using it on a computer that acts as the router and AirPort base station for my network, so it's a relatively complex setup. (Not a lot of rules, but a couple different interfaces to worry about.)

I'm requiring "Network" and "Resolver" in my StartupParameters.plist file.

I am requiring Resolver on an older G4 Powerbook (Ti?) and it has worked up to 10.3.2. I haven't had a chance to install 10.3.3 on the Powerbook yet.

I recently got a iBook G4 and after installing 10.3.3, it stopped working (after logging in, the machine would appear to hang). I changed the requirement of Resolver to Super Server, and it started working again.

To summarize, apparently it works on some systems on some versions of OS 10.3, so don't change anything if it works. But if the problem occurs (after an OS upgrade or otherwise), follow the hint and it should work.