The basic idea behind BrowserID/Persona is that your email address, as stored and authenticated inside your Firefox browser, is your identity. So whenever you visit a site that has Persona support, you get a log-in window pop-up, and all you need to do is click OK and away you go. Yes, it’s much like what we’re all doing with Facebook/Twitter/Google-based authentication now too, the difference is that Persona is browser-based.
Now, Mozilla is expanding Persona with what they refer to as an Identity Bridge for Gmail. With an Identity Bridge, user email authenticity can be confirmed via an OpenID or OAuth gateway. Both OpenID and OAuth are existing open protocol specifications for user identification. The news here is that now Gmail users can leverage their existing Gmail credentials to log-in to Persona-powered Websites.