AFAIK there does not seem to be a way to donate to rust development for the same reasons.

Maybe Mozilla should allow donors to specify the project they'd like to contribute to?

That would give them additional feedback on how the community evaluates their programmatic direction.

Sort of similar reasons; while this is true, it’s also that we aren’t sure how we’d allocate that money if we got it. Discussions about a possible foundation for Rust are ongoing, and these kinds of questions are a big part of why that hasn’t happened yet.

Part of the reason for that, I think, is that Firefox development is done by the Corporation, rather than the Foundation. The Corporation's can have far bigger income streams (i.e. the search engine deal), so it makes sense to make that responsible for the development of Firefox - even though that means you cannot donate to it.