Websites have always had the legal and technical capacity to do this. When you visit a website, it may have embedded code in any given page that tells them what website you have just come from and what site you go to from theirs. They can tell how much time you spend on any given page in their site, and which links you clicked.
This has been a legal use of html code since the beginning of the Internet. That Facebook, a site that generates its supporting income by selling your social media data to its advertisers, has found a way to monetize that legal right to a more nuanced degree should not come as a surprise to anyone.
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