I'm using OpenDNS. I sent them an email regarding this and got a reply from John Roberts (VP):
Hmmmm… since we don't use dynamic DNS for authoritative DNS, I'm not sure this applies.
We accept dynamic IP updates using dynamic DNS API, but from the screenshot, it doesn't appear that pfSense supports all the same fields we use.
http://www.opendns.com/support/category/124
It would be nice to know the proper settings, if anyone has a clue. Or if this could be added to the core that would be great!