They can see what posts you like, what you comment on and which groups you're active in. From that they can extract a profile. Since I've blocked Facebook fro

They can see what posts you like, what you comment on and which groups you're active in. From that they can extract a profile. Since I've blocked Facebook from tracking me around the web, I think their ads have become more relevant for me. They now actually fit in with the activities I follow on Facebook. In my opinion it works better although they might not generate as much revenue for Facebook.