I'd gladly pay to support development of Firefox if it were possible to fund it directly via something like a recurring subscription.
Instead my only option is to donate to the Mozilla foundation which lists the following salaries for their executives (according to Charity Navigator):
Mark Surman, President & Executive Director - $661,886
J Bob Alotta, Svp, Global Programs - $417,327
Angela Plohman, Coo, Secretary & Treasurer - $415,549
Ashley Boyd, Svp, Global Advocacy - $368,445
No thanks. While I don't expect people to work for free there is no way I'm going to make charitable contributions that support those kinds of salaries considering their failed stewardship of Firefox.