Did you know? Despite claiming to block all cross-site cookies out of the box, Firefox automatically allows Google to use them in your browser should you log in to one of their services.
The browser only lets you know about this once it happens, and it’s on you to notice the permissions icon appearing in the URL bar. There is a link to a paragraph on a help page explaining this behaviour, but it seemingly goes unmentioned pretty much everywhere else on the internet.
This surprised me, especially considering Firefox’s stance on privacy. I was even more surprised that this is done without consent. If this is for usability, Firefox should at least warn the user before this happens.
I think the “rest of your tabs” would have to be sites that already include google js (e.g. for “sign in with google” type stuff) to even know you have a google cookie (otherwise what’s the point of FPI/ETP/TCP/network partitioning/no-3rd-party-cookies/etc.), but I could be wrong.