I'm not aware of any non-profit with staffing the size of Mozilla. The problem is that you need to be able to make money and to set it aside for bad times, so you don't have to fire employees the moment the donations falter.

The 501(c)(3) non-profit form of tax-exempt non-profit, which is what the Mozilla Foundation continues to be, is not allowed to do so. That's why they opened up the for-profit Mozilla Corporation subsidiary that does most of the Firefox development.

On the plus side, the only shareholder of the Mozilla Corporation is the Mozilla Foundation, which therefore essentially cannot accept any of the profit the MoCo might make.