have a look around github

the breadcrumbs start here:

https://gist.github.com/MrYar/751e0e5f3f1430db7ec5a8c8aa237b...

https://github.com/search?q=spoof+telemetry

if you know how to do a web search do that. if you cant then sorry about the luck.

The gist talks about disabling telemetry, not spoofing it, and reading the prefs it sets makes it clear that it is actually disabling it.

The github search reports a single repository last updated three years ago, and doesn't appear to even be related to Firefox telemetry at all, as the telemetry appears to be spacecraft telemetry.