The like button actually being present means that your client makes a request to FB to fetch the relevant image resources and JS to display the button. When th

The like button actually being present means that your client makes a request to FB to fetch the relevant image resources and JS to display the button. When that occurs, FB has some limited ability to get information on your browsing habits based on what that like-button JS is allowed to see of your current session (which given browser fingerprinting techniques, can be enough to unify your behavior with high probability across multiple disparate "blips" of signal).