Idk, I think people underestimate what it takes to support a browser. It's a lot of money and Mozilla doesn't have an ad empire to leverage, operating system sales to subsidize from, or phone/computer sales.

All they have is the revenue they make from Google, a little bit from their attempts at revenue diversification, and a little bit from their partnerships (like Pocket). If the Google revenue disappears, they won't even be able to maintain the current level of quality.