It’s around 30 million lines of code. You need actual human beings who have enough knowledge of this code to make decisions.

When I’m on a project with 30000 lines of code as a reasonably experienced dev, I consider that rather challenging to know most details of. This is obviously some complete ballpark math, but that would mean they need 1000 devs.

They had around 750 employees in 2020, after they laid off 250 employees. This includes HR, management, IT support and such, so possibly 650 actual devs, of which not all are working on Firefox.