I can't rember my source so take this with a grain of salt but your browser still connects to telemetry.mozilla.org even when telemetry is turned off and you need to use something like arkenfox or install a fork like librewolf to fully disable. I discovered this after going through a rabbithole when pihole said it blocked telemetry.mozilla.org even when I disabled telemetry

I have found this support page on the matter

They also have no rule against spyware (or at least proprietary software) on addons.mozilla.org