I read that the new layer 3 independant netfilter was here since kernel 2.6.15 but I started having problem with the new 2.6.21. The patch simply substitutes ip_conntrack* with nf_conntrack* where it is needed, the ebuild applies the patch ;)
Created attachment 120317 [details] net-firewall/firestarter-1.0.3.ebuild
Created attachment 120318 [details, diff] files/nf_conntrack.patch
net-firewall/firestarter was removed from portage.