Identify is an addon which lets you see what other social network profiles a particular user has set up (including profiles on Twitter, Blogger, LinkedIn, LastFM, Technorati and many other accounts). While this in itself won’t *prove* whether or not someone is authentic, it might show up anomalies in other social network accounts.

I don’t know specifically what parameters it uses to establish where else you have a profile (though I suspect its more than just spotting your username in different platforms).

In principle, this should work well if you are trying to track people who are online-savvy, though of course for anyone whose not very active online, it won’t be so helpful.

One other thing – if a user makes public their geolocation, that should be an invitation into finding out the extent to which they are who they say they are. Though again, this method’s limited to those who opt in.

Identify addon:
https://addons.mozilla.org/en-US/firefox/addon/11570/