This still doesn’t answer the question. If building Firefox is unprofitable what about Chromium based browser is profitable? Cutting out its base layer development doesn’t change its business viability. Clearly the engine development is not the problem.
Maintaining your own browser engine costs a lot of money. Using the one someone else maintains costs a lot less. It's that simple, plus the network effect, compatibility ...
Okay you've eliminated your browser engine building cost by switching Firefox to Chromium. Now how do you make profit off of Chromium?
My point is that there was no profit model around Firefox so switching engines is negligible. The cost of building said engine is also going to be negligible to the profit returned from the browser. In Google's case this is true. In Mozilla's case they have no model and never had one to subsidize that cost (other than Google search money). Changing base engines turns Firefox into a hobby project managed by a FOSS rather than a serious competing project in the browser-verse.
