I think you're missing the point here: the minority of users simply do not matter. If Mozilla wants Firefox to remain a browser with large market share, it must implement standards that allow DRM. And that's what they want. They don't want to be obscure like Tor Browser. They want to be popular, and they want to have political clout and influence over standards bodies.

That doesn't remove the ability of a minority of users to use something different and make use of the more "obscure" sources, but it does allow the majority of non-technical users who don't care one bit about all this to play the content they want, and in a way that protects their security much better than the old plugin-based approach.