Literally the other way around.

Mozilla can continue to be an irrelevant little NGO with a tiny little office in SF pestering people and shouting into the void and setting up booths at tech conventions on very, very, very little money. A few million a year, much less than they stand to be able to earn from their investment fund returns annually.

Firefox on the other hand requires Mozilla's hundreds of paid full time developers. Its codebase is nearly the size of Linux, as a browser it's constantly patching security issues, adding in new features, fixing things that break for small amounts of the web, etc.

There is simply no organization waiting in the wings that has the money and the interest in making a privacy-preserving web-browser that can just pick up that slack.

They provide like 99+% of the development work. You won't easily replace that with volunteers.

If Mozilla is doomed, so is Firefox. You underestimate how complex Firefox is. It's almost as complex as the Linux kernel.