It is important to note that, reasserting control has to be done at a browser vendor level -- trying to spoof APIs with extensions or whatnot as I mentioned may be a good mitigation for a specific behavior, but it is often detectable in a way that makes it an excellent fingerprint.
Unfortunately, a browser cannot realistically be controlled by a non-corporate-funded entity (if you don't count a government). Modern web browsers are incredibly complex and the web standards are made in a way that largely prevents the creation of new browsers. Firefox is mostly funded by Google, and Mozilla being the ineffective organization it is, this is unlikely to ever change.
