It is about "Delegated Account Recovery" which is originally proposed by facebook.
https://www.facebook.com/notes/protect- ... 2090271267
As you can see in Bug 108049, a little bit more background is like this;
"Account Recovery" is common problem for most online services.
When users forget their own passwords and lose access to their own account, "Account Recovery" make it possible to regain that.
"Account Recovery" are usually implemented with recovery questions or sending a link to your email or sending a security code to your SMS.
"Delegated Account Recovery" could allow you to choose an alternative method with third-party web site as Recovery Provider.
I think this is pretty much interesting protocol. If you feel so too, please vote for Bug 108049.