Okay, listen up:
Mozilla is two different entities. The Mozilla Corporation and the Mozilla Foundation. The second one? That's the social good one you really want focused on important things.
The Mozilla Foundation, like all non-profits, publishes their Form 990 annually to disclose compensation. Here it is.
You'll see that the top earner there, Mitchell Baker, who is very handsomely rewarded, is actually paid by the Mozilla Corporation, not the Foundation. Put another way, the non-profit is not blowing its funding on a CEO.
And the corp, by the way, is a wholly-owned subsidiary of the Foundation. It exists to generate additional revenue for the Foundation. That's a good thing too, because donations alone won't cover operating expenses.
The annual report of the Foundation shows a pretty healthy financial situation, and increased investment in public good projects year-over-year.
I don't like everything they do either (e.g. that risible website generator), but I don't actually think they are suffering from a lack of focus. They're suffering from a mature market.