Part of the "problem" is that people don't care about any of those products, except Firefox.

Mozilla needs to figure out how much they need to maintain Firefox, nothing else. I suspect that's not the entirety of the $200 million they currently spend on "development costs". Everything else they receive in donations and partnership fees should go directly into an investment portfolio which will be used to keep Firefox development active in the future.

If they didn't care about anything else, the Google money could fund Firefox for at least two years per yearly fee.