This requires having the Facebook mobile app installed though which is responsible for running the background service. If one doesn't have the Facebook mobile app installed, this doesn't work the way it is described?
How do Facebook and Instagram apps track what you do in the browser, even in incognito mode?
Meta apps start a local server on the phone and keep it running in the background. The Meta analytics script, running on most websites, pings any "localhost" server with the anonymized tracker ID for that session. The app then associates the browser ID with your Meta account, and voilà, all your browsing history is now linked to your Facebook account.
Android is designed to block such things, but Meta found a workaround using basic Sockets and transmitting the tracker ID in the initial handshake of a WebRTC (voice call) request. It's genius and evil as fuck.
https://www.zeropartydata.es/p/localhost-tracking-explained-it-could
Discussion
Facebook (confirmed), Instagram (confirmed), WhatsApp (unconfirmed), Messenger (unconfirmed), Threads (unconfirmed), etc...
I guess I'm not too shocked by this. Any company in the ads business is probably doing something similar. It's a good thing I don't have Instagram or Facebook installed on my device and haven't visited the site since 2017.
The native app is basically running a background service that the web pixel connects to. So it isn't really a problem with web browsers.
i disagree
It will work just as well with meta's other apps like WhatsApp, Instagram, etc
But yeah, it requires the company who wants to track you to have an app installed and running on your phone.