As many commenters have pointed out, Facebook (and a lot of other sites) have many myriad ways to track you, and so something such using private browsing mode w

As many commenters have pointed out, Facebook (and a lot of other sites) have many myriad ways to track you, and so something such using private browsing mode was insufficient to protect your privacy. What should trouble you, however, is that this sort of correlation is going on all the time in the background. It's not necessarily always the case that the correlation is made apparent to you. Often times (most times?) it will be totally invisible.