Mozilla could solicit donations for the development of Firefox while also still being able to rely on commercial funding sources if they restructured the Firefox project so that the core technologies underlying it (stuff like Gecko and SpiderMonkey) were actually developed by the Foundation instead of the Corporation, while the Corporation could package all of those pieces together into a complete software product with branding. The way things are now, though the entire browser is developed by the Mozilla Corporation and so its development can only be financially supported by Mozilla Corporation selling products or engaging in business deals.