I tested my IPv6 access :
I introduced a firewall rule on my HENET interface :
I have a DNS record that point's to my WAN IPv4, not my WAN IPv6, so I had to use my IPv6 WAN IP to connect to the GUI.
I had a cert warning from my browser, of course.
But the access worked well :
"Well" means for me : knowing that my IPv6 is using a tunnel to tunnel.ne.net (Huricane IPv6 ISP) the speed was somewhat limited, about 10 Mbytes /sec.
I could browse the entire pfSense GUI very well, no hick-ups ....
edit : I'll leave the IPv6 access open for a while.
PM me, and I can even send you an 'access' so you can test drive yourself.
That is, if you promise not to change something, as this is a "live' environment ;)