Big difference to the Wikimedia Foundation is how much money they need. The Mozilla Corporation (which develops Firefox) has around 750 employees.
Optimistically, only 500 of those are devs and work on Firefox. If you pay those a wage of 100,000 USD, that makes 50 million USD of costs just for wages.
Firefox has less than 200 million monthly active users, so everyone using it would need to donate $0.25, or alternatively 1% of users would need to donate $25, yearly.
That’s a lot of money to hope people donate, and this is a very optimistic ballpark estimate.
There’s two alternatives currently in development, inZOI from the PUBG devs, and Paralives from a smaller indie studio.