How much effort do Chrome and Android require from a company the size of Google? It's a genuine question.
Jolla/Sailfish make a mobile operating system with a handful of people, and even though that system pretty minimal, I'd say the added value on the Android side is the ecosystem of apps and porting to devices, which is done by other developers and manufacturers than Google. And I'm not sure how many people work on Firefox itself on any given day.
I guess it's just really hard to get a clear picture on what all those people in large companies are really doing day to day. The overhead must be enormous, and likely a lot of engineering effort is thrown at the wall to see what sticks.