As a bit of an aside, I learned recently why Mozilla has the weird Corporate/Foundation structure that it does: https://news.ycombinator.com/item?id=47701441
Basically the IRS is highly skeptical of the idea that free software development fits the legal definition of a 501(c)(3), and tends to reject such applications [1][2]. That is why Mozilla Foundation cannot use donations for Firefox development, and instead uses them for activism.
Someone claiming to be the CEO of one of these foundations appears to confirm it. Just thought people might be interested to know since this comes up in pretty much every thread about Mozilla.