"we're really, really easy to implement" "I want to see us become the de facto auth solution" "We also let you reach many, many more people" "but we're also a really nice option to put alongside your social login"

Assuming by "we" and "us" you mean Mozilla? Or do you also mean the other major browsers?

Why did you write it like that? Why not just say "Persona" instead of "we" and "us"? Surely Persona is much bigger than Mozilla or do you not think so?

Firstly, that kind of language does not inspire trust. It sounds very much "us" vs "them", instead of addressing the real problem, which is helping users by creating and managing more secure passwords.

Secondly, your marketing to users includes:

"Many sign-in systems carry your profile data with them; some even share that info with other sites and social networks. We believe you should control how your personal information is shared."

You seem to want to attract publishers and yet you show your distrust of them to users.

Also, from experience in Public Web Apps, and the fact that it's still not possible for a user to give raw and pure TCP, UDP or POSIX power to Web Apps (and WebSockets and IndexedDB are not at all the same), I don't think the issue is so much that the user has power, as it is that the browser should have power. As it is today, the user is given very little power at all by the browser. Very little trust. Most spec discussions seem to constantly worry about users shooting themselves in the foot, and are prepared to stop at that, rather than finding ways to empower users to give power to web apps.