In most donations, you're donating to the product as a whole. There's no way to ever know where your money explicitly goes. At least I've never seen a charity operate that way.

Even if you did donate to development, development is not averse to administration, marketing, hiring, and diversity. And developers are not spending time at Firefox getting the product in the hands of people so it can get better with feedback. Marketing and all the other areas you find "problematic" are trying to do that.

Either way, even if your money doesn't go where you want it, that's a bad reason to not donate considering there's no indication that their product is substantially inferior to competition, they're making hugely poor decisions, etc.