Everyone I know who works on Firefox says their team is understaffed and people are not always being replaced when they leave. They could stand to invest a lot more (or more efficiently) into their core product.

Could they hire more people to ask Firefox users what they want Mozilla to work on? They’d probably say Firefox features and bug fixes. There are people who could do the work in exchange for some of that money. I don’t think this is a case of too much money chasing too little profits, which seems to be what you’re suggesting.