>How did Mozilla survive as a business?

On one end by almost literally being an extension of Google. On the other end by constantly laying off engineers. A big problem people are just handwaving away is that browsers are incredibly complex nowadays and how do you fund development of a browser engine? If you think the "Linux" model would work, well browsers already have that - it's called Mozilla and there is never any good news about them.

Brave is also funded by Google - Brave doesn't develop a browser, they develop a skin around a browser engine that Google pays millions to develop and has decided to open source.