1B is very little. I would focus on your other point:

So when resources are diverted away while there's still work to do, you should see red flags and look for better focus right away.

I'm not sure 1B is very little - it's thousands of programmer-years. It is weird to characterize 1B over 3 years as "billions" unless there are substantial funds coming from other sources.

That's the vast majority of Mozilla's income, you can check the publicly-available financials. It's small potatoes compared to the companies Mozilla competes against: Google, Apple, Microsoft.