I'd love to donate to Mozilla, but I'm concerned my money could just end up in some C-suite pockets if I do. Is there a way to donate specifically to Firefox core(-ish) team, and maybe also MDN?
However, dollars are fungible. If you donate $500 to support MDN, that may replace $500 for MDN coming from revenue, which frees up $500 to go into something else, like a C-Suite's pocket, or Pocket or whatever. So while your dollars go where you said, it still enables whatever you didn't like. OTOH, if you donate $50B to support MDN, that's a bit different; it certainly frees up whatever money was going to support MDN before, but there wasn't $50B of MDN expense, so the excess beyond the needs of MDN doesn't go anywhere.