Pretty rough, but that's not a too unrealistic scenario given that Google is a pretty aggressive competitor in the browser market and there are hardly any other

Pretty rough, but that's not a too unrealistic scenario given that Google is a pretty aggressive competitor in the browser market and there are hardly any other search engines that would be good enough to be the default in a mainstream browser. (Mozilla tried with Yahoo but they couldn't deliver the quality users have come to expect.) Have you checked Mozilla's expenses too? It has around 1200 employees, I think, and a few offices around the world, data center costs etc.. If you want to be able to independently keep that going for a few years, you need a big war chest.