Facebook has such incredible smart engineers that they can file patents to identify you based on the dust of your camera lens [1]. It should be a cinch to them not to track such third parties in any way, shape or form.

The problem was that they gave zero fucks about the privacy implication to third parties, which have nothing to do - and no business relationship with Facebook. It seems quite the opposite: That the go through great length to maintain shadow profiles and track everybody.

I really hope that the GDPR forces them to clean up their act.

https://gizmodo.com/facebook-knows-how-to-track-you-using-th...

For instance, it could still be legal for Facebook to slurp your friend's address book (and your profile, indirectly), but the regulation could require them to discard and purge that information if they can't immediately match it to an account.