The big question is:
Does the money go to Firefox or to funny projects and (what I consider) insane exec salaries?
Yes, Mozilla (.org) is a non-profit, and Mozilla (.com) is a regular corporation. Yes, Mozilla has commitments about transparency. Yes, exec salaries are insane.
Do folks who ask this question scrutinize every purchase or business they make to this degree? In the laundry list of entertainment, learning, and professional subscriptions, what portion of spotify, github, or other popular subs end up contributing to just the feature or service you like as opposed to the entire organization and other initiatives that the organization supports?
However, when you're giving to charity, what are you getting? You probably want to know.
If charities are smart, I bet they could take advantage of this by creating classic ladders which encourage more contributions if people get a say of where a "portion of their donation" goes.