But wait... can they still identify you that way? I'm not on facebook, so maybe it's moot in my case. But are you saying that blocking third-party cookies is not enough to keep facebook from tracking your other browsing activity?
Technically Facebook can by using the requests your browser sends for their ubiquitous sharing widgets on many websites. Your browser very probably has a unique fingerprint¹, so you might want to block those widgets as well (Privacy Badger does this).
Because Facebook's profits come from advertising and that understanding our browser habits is a requirement for their core business, it is not too far-fetched to believe that they track non-users as well.
Every time you go to a website with the Facebook like button, they see your IP address and the website you're on. Go to enough websites from that IP address and they can get a good idea of what you like. In addition, it is very easy to get your real address from your IP address, or at least your general area. Combining these gives them a good idea of who you are.
