Note that charitable donations (of the 501(c)(3) variety) in the U.S. can only be employed for a very specific whitelist of purposes, and software development and marketing are not among those (the Mozilla Foundation uses donations to fund things like education programs instead). If you're a software developer who's interested in the health of Firefox specifically, consider instead donating your time by volunteering (not limited merely to Mozilla or Firefox; there are dozens of open-source projects whose development directly or indirectly ends up benefiting Firefox).