Sounds like they copy pasted my demo into production: https://robinlinus.github.io/socialmedia-leak/
I already had Privacy Badger and had disabled third-party cookies, but it's good to have confirmation that it's working. I'm showing up as not logged into anything, even though I am, in fact, logged into six of those services (including HN, obviously).
I am logged in to HN and it didn't catch that.