[ken]

Why does it have to come from any of these?

Companies need web browsers (and their component parts), too. They're going to pay engineers to work on them, anyway. That's how development is supported for Linux, Git, Postgres, Ruby, etc.

If every Git command started displaying ads tomorrow, would you say that that's "unfortunately inevitable" given that people expect version control to be a free product, and that the Git developers need to be paid somehow, and there's only 3 possible ways for that to happen?

("It was not a paid placement or advertisement", they say, so it's doubly strange to try to excuse it as a necessary revenue source. There is no revenue for Mozilla here.)