Google Chrome is adding a new feature that lets their browser target you with ads without using third-party browser cookies.
Here’s some more info: How to fight back against Google FLoC.
But basically it comes down to: if you’re a web user who doesn’t want your browsing history to be used to target you with advertisments, stop using Google Chrome. There are many alternatives. I’m a Firefox boy myself.
For site owners, you can add a
Permissions-Policy: interest-cohort=() response header to opt-out of your site being included in the data collected about your Chrome visitors. I’ve updated this site to add the header.
[Update 4.18] sierdy.one says the fears about FloC aren’t exactly accurate, and that webmasters don’t really need to add the response header as long as they aren’t using third-party scripts anyway? I’ll just keep it around though.