But that's the whole point: they
did pay their medical bills. It's not like they didn't pay their medical bills and instead bought a ps5. They did both.
Mozilla develops Firefox, and they also pay their CEO a lot. Their CEO may be overpaid, the company may be mismanaged, but at least they are still upholding their commitment to maintaining Firefox. Picking out one expense that you don't like and saying "all the donations go to this, see!" is just disingenuous.
Whether donating is worthwhile is another question, and it seems like the answer would be no. But it is a very different thing to say "All the donations just go to the CEO" instead of "I think the CEO is paid too much".
We could also cherry-pick in the other direction and say the CEO is negotiating deals to bring in the 90% of non-donation revenue of Mozilla, in which case you could easily say that his pay is a result of that revenue creation.