Just visit the site, get an infinite session, and voila!

Logging in from a different machine? Cleared cookies? No problemo - to restore your session, get a notification, click it and session restored!

This is the poor man's "iCloud" also. Basically your google login or firefox login is your master login. It's basically same facebook connect - another identity provider. Move over personas! We've got a new OpenID in town. Except instead of email providers it's the browser vendors.

NOTE: This doesn't solve the problem of power dynamics -- browser vendors are still pretty centralized -- but does make it super simple to let users of these browsers get a account on a site without an email, mobile number or password, at least on the desktop.