Mozilla is an open-source project. When an open-source project somehow loses its way, it's often forked by a new team of contributors who have a better idea. This happened several times: Open Office / Libre Office, MySQL / MariaDB, X86 / X11.org, hell, even GCC / egcs in the 1990s.
But this likely cannot happen to Mozilla, which is basically kept afloat by Google handing it some money for keeping it as a default search engine, about $400M a year currently [1]. There is little chance that an alternative "Better Mozilla" organization would collect as much, or at least half as much, to support a fork. It would e.g. take 33M users who agree to pay $5/mo for a Mozilla "support subscription" to collect $400M a year.
Maybe a web browser can be maintained for less than 400M, but likely not much less. The modern web is fiendishly complex, and you need both a desktop version (three platforms) and a mobile version.
[1]: https://www.pcmag.com/news/mozilla-signs-lucrative-3-year-go...