$190k/y cost doesn't mean an engineer
earns $190k/year. Not even close. I'd guess that means they're around average $140k/year income - which really isn't that high for engineers, especially since they have a large presence in the Bay Area.
The other expenses break down into mostly marketing ($47M) and "general and administrative" ($59M). The first one makes sense - it's a small budget for a global presence. G&A usually includes office rent, which I'd bet is a huge chunk.
Let's do the math: SF is ~$80/sq.ft. Usually assumed is $175 sq.ft/engineer. That's $16M of those $59M. Then there's utilities, insurance, etc. Let's call it $20M.
Then there's legal expenses - those usually go into G&A. Given that in 2016, Mozilla squeezed $1B of payments out of Verizon ($375M/year until 2019), I'd assume some lawyers made a good chunk of money. Given the huge jump in G&A from 2015, I'm willing to attribute the entire difference ($20M) to legal costs. This was a huge one-time event, it would make sense.
Now we've explained $40M of those $59M. So, at this point, we're debating if the remaining $19M could possibly have been extracted nefariously. Likely, no, because there's more costs. And if you have 1,200 employees, costs add up quickly.
Meanwhile, the only evidence you've brought for your accusation is "because I believe it's true". That's not even close to meaningful. You're certainly entitled to your own opinion, but the facts we all share say otherwise.