Technically Facebook can by using the requests your browser sends for their ubiquitous sharing widgets on many websites. Your browser very probably has a unique

Technically Facebook can by using the requests your browser sends for their ubiquitous sharing widgets on many websites. Your browser very probably has a unique fingerprint¹, so you might want to block those widgets as well (Privacy Badger does this). Because Facebook's profits come from advertising and that understanding our browser habits is a requirement for their core business, it is not too far-fetched to believe that they track non-users as well. 1: https://panopticlick.eff.org/ https://panopticlick.eff.org/