Does Firefox sell your personal data?
github.com
github.com
With the being said. Firefix does make it pretty easy (but not obvious, requires some tedious edits in about:config) to disable most of their spyware.
Tor browser, ungoogled chromium are good choices. Other see reddits such as https://www.reddit.com/r/browsers/comments/11by0m7/what_is_t...
By the way, it would be wonderful if you or someone could link to detailed instructions (or maybe even just a script you can run or something) about those tedious about:config edits.
I had been putting one together based on it for newer machines (and it worked great), but just now when I went to look for it, I'm not sure what happened to it. Sorry I can't share mine.
If I recall correctly, you just plop the user.js into your profile. You'll want to do it from a fresh profile* and then any time you want to make a change, you'll make it in user.js instead of about:config. What I believe happens is every time Firefox start, it applies all the configuration options specified in your user.js.
Data mining gold galore, not unlike Yahoo's acquisition of the "free" Delicio.us back in the day.