We should be able to directly donate to fund the salary of full-time engineers working on Firefox and only Firefox, completely circumventing the PMC.

It might also be possible to fork and spin off Firefox into a new non-profit, circumventing Mozilla if some of the devs organize it.

> We should be able to directly donate to fund the salary of full-time engineers working on Firefox and only Firefox

Money is fungible. If you want to do this, frankly, donate to LibreWolf.