It's probably not cookie-based, or not only cookie-based. Browser fingerprinting...

tarboreus on Aug 28, 2017 | parent | context | favorite | on: Ask HN: How does Facebook know what I buy on Amazo...

It's probably not cookie-based, or not only cookie-based. Browser fingerprinting and user profiling have gotten very sophisticated, and don't think the big 4.5 aren't using these techniques extensively.