If you want port forwarding, they recommend that you do... something. It's not clear what; what you can find on the internet is mostly just people complaining that they insisted to customer support that they needed port forwarding, customer support said they'd do that, and port forwarding still doesn't work.
But, intriguingly, it turns out that a Comcast router will also assign every device on your network at least one public ipv6 address. They also firewall all incoming ipv6 traffic, but unlike the situation with port forwarding, you can disable that firewall on the router admin page. (You can't put up your own firewall.)
