Seems to be some sort of Mozilla initiative: https://browserid.org/about and https://support.mozilla.org/en-US/kb/what-browserid-and-how-does-it-work Anyone?
sounds like an alternative to OpenID never been too fond of services like this as although it might be more convenient, 1 security breach means the hackers can get all the juicy logins for all sorts of websites from 1 place
I noticed that NoScript added it to default whitelist in latest dev (2.2.9 RC2) update's chagelog. http://noscript.net/getit#devel I removed it again, until I decide.