How well it works depends on your setup, in my case I use a routed configuration, I'm unsure if bridged would be better.
The basic gist is that pfSense wants to be allocated a /64 via prefix allocation via a router advertisement (SLAAC or DHCPv6). Only in this configuration can you set the LAN interface to track the WAN, which allows you to use a single /64.
Sadly there isn't a dedicated server provider out there that I know off that cleanly supports this configuration.
In almost all cases you'll have to manually assign subnets inside the /64 (ie a /65 for the WAN interface and a /65 for LAN) so you can route around traffic. It's a bit annoying to setup but possible.
(It's still much better than OVH's IPv6 support which is just plain broken)