There are two "Firefox"s:
- Firefox, the code base.
- Firefox, the compiled binary of that code base.
The codebase remains open source under the MPL while the binary explicitly, by Mozilla's own admission, is not. They are source available.
From the very brief skim I did of your post, it looks like we're on the same page. I had a few people who don't understand open source licenses come at me in my Lemmy replies when this was first unfolding. Ultimately it's on them to understand their agreements.