It is actually possible and Facebook does do it. Everywhere you see a facebook like button, javascript is loaded from Facebook. Facebook logs certain browser ch

It is actually possible and Facebook does do it. Everywhere you see a facebook like button, javascript is loaded from Facebook. Facebook logs certain browser characteristics[1] with the request and uses this to identify you. Then when you log in it can match your account(s) to your browser identity. There's more complex data mining going on at Facebook but it is happening. [1] - https://www.eff.org/deeplinks/2010/01/tracking-by-user-agent https://www.eff.org/deeplinks/2010/01/tracking-by-user-agent