One big thing to keep in mind about Facebook et al, is that every page with a like/share/whatever button from a third party effectively allows said third party

One big thing to keep in mind about Facebook et al, is that every page with a like/share/whatever button from a third party effectively allows said third party to build up a profile of who the person operating the computer is. Even if you do not have a Facebook account, Facebook likely has a shadow profile on you based on browser fingerprint etc showing up on various sites. Also, your typical adblocker is not configured to block these buttons by default.