In case of Mozilla, those passive users generate money due to Mozilla's global search collaborations, which feeds into the development of Firefox: https://www.feedough.com/mozilla-business-model/
You don’t need $100 million a year to develop a browser, though. Much of that money seems to go to other projects.
Diversification, in order to attract other sources of revenue apart from search engines (which can easily disappear once an agreement expires). Relying on just a single source of income is never a good idea...
Unfortunately, a complex piece of software like Firefox is not easily maintained (status quo) or further developed (adding new features) using a purely hobbyist basis.
There seems to be no shortage of forks already: <https://en.wikipedia.org/wiki/Category:Web_browsers_based_on_Firefox>.
How much do those forks rely on the base project to add features, develop the rendering engine, etc? If the base project stops, how many of these projects will continue to exist? Cheers, Peter -- Peter Reutemann Dept. of Computer Science University of Waikato, NZ +64 (7) 858-5174 (office) +64 (7) 577-5304 (home office) http://www.cms.waikato.ac.nz/~fracpete/ http://www.data-mining.co.nz/