As far as I can tell Mozilla does not have a spot to select what the donations go to. I haven't gone past the first screen on the donation page so maybe its fur

As far as I can tell Mozilla does not have a spot to select what the donations go to. I haven't gone past the first screen on the donation page so maybe its further down the process. They do have the option to send a check so you could restrict it for only Firefox development but any money that is not restricted is fungible. This means if I donate $100 for Firefox development they can take another $100 (that is not restricted) that they would have used on Firefox on something else. Most people do not mark their donations as restricted so I would still for all intents and purposes be funding something other than Firefox.