The Mozilla Foundation does lots of "spreading awareness" but does not contribute to Firefox development.

That is the most vexing part. I want to donate for Firefox development. Not marketing, not side projects, let me just fund the devs. But no, that is not possible.

Blender is a huge success story relying on sponsors and donations, Wikipedia is swimming in money but no we can't just have a free browser.

No we need to have a Mozilla Corporation that lives on Google money for being the controlled opposition i.e. technically avoiding monopoly situation thing. After all CEOs can't get rich on donations, can they?