If I try to create an IPv6 firewall on Ubuntu 14.04.3 using the "Block all except ports used for virtual hosting" option the "Setup Firewall" button, then Apply Configuration I get the error messages:
ip6tables-restore v1.4.21: unknown option "--icmp-type"
Error occurred at line: 34
Try `ip6tables-restore -h' or 'ip6tables-restore --help' for more information.
That line 34 is:
-A INPUT -p icmpv6 -m icmpv6 --icmp-type echo-reply -j ACCEPT
According to http://manpages.ubuntu.com/manpages/precise/man8/ip6tables.8.html
the option should be --icmpv6-type not --icmp-type so I suspect that's the cause.
Thanks - I'll fix this in the next webmin release