FxA is primarily for Firefox's own products and services. Mozilla Persona (confusing name - personas is what they called firefox themes as well) is closer.
Yea but there's really no good docs for Persona around anymore, that I can find.
The plan is to use Persona for ones FxA:
> One we get the basics down and enable single sign-on for relying Mozilla Services with your Firefox Account, we hope integrate Firefox Accounts with Persona on the Web and Firefox user agents to make logging in everywhere as painless as it should be.