1. Zero telemetry. I mean ZERO: remove all telemetry code from the codebase. They can ask me about features the old-fashioned way - surveys!
2. Focus on privacy and security. Put these to the top of the list.
3. Stop paying your CEO millions! Not worth it imo!
4. Stop with all the other Mozilla shit! I am interested in a browser (and perhaps an email client... I'll let you work on that too!). No more Pocket, VPN and all that other shite.
5. ZERO, I mean ZERO data capture at all! Nothing. Not a single bit except when someone clicks the link to download Firefox, you can capture their userAgent and whatnot. But the browser, Firefox, should not be capturing a single byte of data from me once installed (except perhaps a periodic version check and you can pass in the version like this: https://firefox.com/update?v=123.568).
6. For sync, allow me to sync an encrypted file to Dropbox, OneDrive, Local drive, Whatever.com. That way my passwords, bookmarks etc. can be sync'd from MY location that I control, not yours!).
7. Have a "Block all shady JS tactics" button. This would include fingerprinting, location and such. Perhaps you could send bogus, random data when it's asked for instead. That'd be fine too.
I think that's it :)
For a browser that did this, and was properly audited to prevent anything shady from creeping in, I'd pay $30 a year for it.
Edit: To clarify - I wouldn't pay the current Mozilla a single penny!