Does Firefox do reproducible builds? This bug report makes me think it doesn’t (at least for Linux): https://bugzilla.mozilla.org/show_bug.cgi?id=885777

But maybe they do for Windows/Apple/Android?

A source for what?

https://qutebrowser.org/ and Librewolf

It was probably Chick Tracts: https://www.chick.com/products/tract?stk=0046

That doesn’t detract from OP’s point. I want Mozilla to be a good, privacy respecting organization, but they aren’t anymore, and chromium has nothing to do with that.