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?

Ironically Wikimedia is also throwing money around to side projects, outreach, etc. But luckily for them their products are essentially run by volunteers.