C6300v2 and ipv6 firewall question

Just converted from a C3700 to a C6300v2. I'm on comcast cable and I notice that the default setting for ipv6 under Advanced is for that checkmark to turn OFF firewall.  Is that something I should reverse?  I'm assuming they want it that way as setup by the config file?  What defenses does this modem already have built in?