Im 100% certain there is enough funding going to mozilla that is specifically intended to help firefox. All those donors, private and commercial, could/would switch if the public stunt of declaring mozilla a sinking ship is aggressive enough. I dont believe for even a second that more than 5-10% of mozillas money is going towards actual core firefox/thunderbird dev work. Its not cheap to develop im sure, but nowhere near the amount of money that mozilla sucks up every year.