Google make up a significant part of Mozilla's income, but Firefox development doesn't make up a similarly significant part of Mozilla's expenses. They could keep browser development going without issue even if Google ditches them.

Firefox has such a small slice of the browser market, that I doubt Google will bother.

You mean Google won't bother paying them anymore?

You don't think Google is spending all that money for nothing, do you?

It has long been argued that the reason Google pay to support Firefox (by being default browser) is to keep it around and so avoid being treated as a monopoly. That seems reasonable.

Though now a bribe to Trump/Musk should be enough so maybe they don't need FF anymore.