I wonder why the current structure is set up like that. I mean I don't think it's by accident – if it were set up like that by accident, surely, it could have been set up so people could direct donations directly at Firefox, if the CEO wanted that.
Also Mozilla Foundation didn't qualify as a public charity since it received less than 1/3rd of its revenue via donations, though I don't know if it can be considered as one now (15 years after the split).