One way would be to keep forking Firefox's codebase for bug fixes and new features while customizing it to fit the needs of the privacy conscious users. It may not be "ethical" but it will serve the main premises of open source and is also doable as a community. A new name would also be required as Firefox is trademarked by Mozilla (See Iceweasel Browser [1]).
[1] https://wiki.debian.org/Iceweasel