Looks like fwbuilder does not currently support ipv6:
It creates scripts with the following lines:
ip6tables -L -n > /dev/null 2>&1 &
I’am on an ipv4 network so I could just have forget about this. But there is problem with Java applications. InetAddress.getLocalHost() returns an ipv6 address (see java.net.InetAddress sources).
A workaround is to remove the “ip6tables” lines from the firewall script and leave all the ipv6 traffic open.