CEO of Mozilla earns $3m/year.

https://news.ycombinator.com/item?id=30665913

If the Mozilla foundation creates a donation button with the condition that the money goes solely to browser development (no CEO salary or political activism) I will donate.

Except that it's well-known fact that none of your donations for the foundation ever go anywhere near Firefox itself, since Firefox is spun off as their commercial sector to accept Google's money

that doesn't pay for Firefox...

I donate to them as well, but donating broadly to the Mozilla foundation isn't the same as selling the web browser in exchange for money.