100% agree.
If its not open source 1) you can't fully trust/audit. and 2) you'll be left in the dust should the company cease to exist as nobody can continue development.
If Firefox is not private enough use Librewolf. If you're interested in something new and exciting give Zen Browser or Floorp (both based on Firefox) a spin.
check out Give up Baby Go by Peach Pit - if you like it you'll probably like their discography.