The goal of FireStarter is to provide easy to use, yet powerful, graphical tools for setting up, administrating and monitoring firewalls for Linux machines.
Firestarter has not been updated since 2005. It is abandonded by the developers, doesn't support IPv6, makes mistakes (such as creating a rule for both tcp and udp when you only wanted tcp) and possibly contains security bugs. Google for "linux firestarter abandonded" and you'll see plenty of hits. It's sad, because Firestarter was a nice piece of software.