Exactly that. If they got rid of their hobbies then this sort of scam wouldn't be necessary. Yes, it's a scam: bait and switch.
Mozilla Corporation (which is where your donations go - you can't donate to Firefox as such) is a taxable, profit-making company.
Mozilla Foundation wholly owns Mozilla Corporation, and is a non-profit. But you can't donate to Mozilla Foundation.
(I don't know how you can be a non-profit that wholly owns a profit-making corporation; I'm not an accountant, and I'm not familiar with US tax law)
The history of Netscape and Mozilla is sufficiently farcical to fuel an entire 6-series comedy franchise. Were it not for the jaw-dropping salaries that the absurd execs draw, I'd laugh.
And Harvard has a multi-billion dollar endowment that they hoard. Mozilla is doing it wrong.
Harvard endowment is so huge for two reasons: (1) fundraising, (2) earning more than 5% per year for long, long, long time. But they still must spend 5% per year of their massive endowment.
Running a non-profit with only an endowment (no fund-raising) for more than 20 years with is hard to do.