This is from a year ago, but I didn’t see this level of persistence in gathering telemetry before. I am blocking most mozilla tracking endpoints via host file, but that’s a bit extreme.

Apparently you can create a custom preference to block it:

The good news is that it is possible to turn off telemetry-coverage if you are one of the lucky 1% selected to have it installed. To do so, you need to manually create a preference to opt out of Firefox telemetry antics a second time. Information on how to do so isn’t so forthcoming, either. It’s buried in the bugtracker for the telemetry-coverage system add-on but has been tested as working by Mozilla’s devs: