Cue the lawyers ... Re: Big Hoodie
Depending on the site's ToS, the fact that FB is monitoring and tracking non FB subscribers may be a violation of the ToS and agreement w Facebook.
Again this shouldn't be a surprise and why many w NoScript block FB scripts.
Of course not all browsers work w script blockers and addons.
This could be a major Class Action lawsuit against FB since none of those who were tracked gave permission for FB to track them.