Yes I get your point. Some software can run without a large income stream, on a volunteer basis.
You’re using that fact to say that Firefox also can. And if you care to look at my profile you’ll see I’ve argued time and time again that Mozilla is an overblown organisation and should be slimmed down to a couple of hundred, working solely on the browser.
I doubt, however, that you can build a modern, up-to-date browser on a volunteer basis.