Native IPv6 firewalling is only supported in kernel versions 2.4+. In older 2.2- you can only filter IPv6-in-IPv4 by protocol 41.
Attention: no warranty that described rules or examples can really protect your system!
Audit your ruleset after installation, see Section 18.3 for more.
Since kernel version 2.6.20 IPv6 connection tracking is fully working (and does not break IPv4 NAT anymore like versions before)