I've never made the exact criticisms above but I've got the solution. Taking the money from Google is fine. Stop spending it all. The CEO doesn't need an inflated salary, Mozilla is not a tech giant. Mozilla doesn't need pristine expensive offices in HCOL areas. Mozilla could pay a core group of engineers good salaries, work on Firefox and adjacent tech like servo. If they had done that and banked/invested the rest of the cash they'd have a big runway for the future.
How many is core? I don't know. Not 750 though. To change course now would mean layoffs which nobody likes. But I argue they never should have hired that many folks, and to continue with that headcount is throwing good money after bad.
If the purpose of the Mozilla organisation was to fund Firefox into the future then they have catastrophically failed at their job. If their purpose was to spread the money they had around to a bunch of people as quickly as possible before it runs out, whilst putting on a good face, then they've succeeded 100%