Mozilla is not a browser producer, it’s a general internet charity that earns money by producing a browser. Most of their income goes to charity and reserves of which they have about 1bn – roughly four times as much as wikipedia just for a sense of scale, wikipedia doesn’t do any business deals to get at cash but instead does annoying donation drives.

They could scale down significantly while still keeping firefox development ongoing, they probably wouldn’t have much issue finding enough donations to fund development, but the strategy seems to be building reserves and diversify commercial income, things like the revenue share they get from pocket for sending people to ad-ridden pages.

When you’re currently donating to Mozilla you’re not donating towards Firefox: Mozilla-the-company can’t receive funds from Mozilla-the-foundation, those donations are going to charity work.

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And, to make this clear: None of this is a grand revelation, or new, or outrageous, it’s basically always been like that and it’s always been a perfectly proper way to run a charity. Most of the recent pushbacks comes from people hating that Mozilla funds stuff like getting women into STEM, being outraged that the wider Mozilla community is not keen on having a CEO which opposes gay marriage (very staunchly so), etc.