There is nothing about how charities work under US Federal tax law that would produce this result.
Tax-exempt charities (which must by definition be non-profit, but not all non-profits are charities, and not all charities are tax exempt!) must spend money in a way that's aligned with their mission, and there are rules on how much they can spend outside that. (The really big no-no has to do with political lobbying and the endorsement of candidates for public office -- a relic of a more civilized age when apparently we thought that should be left up to individuals. But I digress.)
The Mozilla Foundation is a California corporation with tax-exempt status under US Internal Revenue Code 501(c)(3), which covers "public charities, private foundations or private operating foundations". There are slightly different rules for each category.
I'm not sure what category Mozilla Foundation is; my suspicion is they are either a public charity or a private operating foundation. In either case, there's nothing that would prohibit them from funding software development, as long as it doesn't unfairly benefit someone involved in the organization's governance.
Their 2016 financial statements (I couldn't find anything newer) are available:
tl;dr: In 2016 they spent over $250k on software development as a line-item, out of about $500k in revenue total. It's by far their biggest budget item.
> tl;dr: In 2016 they spent over $250k on software development as a line-item, out of about $500k in revenue total. It's by far their biggest budget item.
The numbers are actually $250 million and $500 million. All the tables this report (as well as a newer one I have to search the link for) list the figures in thousands.
I'm told that this is incorrect and that the FSF has been doing it for 34 years, the EFF does it, the ACLU has done it and others have even paid for proprietary software development (their apps etc).
i worked for mozilla, your donations pretty much do not go to coding firefox. there are side effects where it will affect code, or someone that gets employed by foundation that will now have money and free time to code for firefox for free, but its not like "your dollars go to hiring a sw engineer".
the donations are still useful though because if there were none mozilla foundation would die, and in turn, mozilla corporation would also die or be sold as its fully owned by the foundation
I don't think it's for those reasons, but the outcome is the same -- money donated to the Mozilla Foundation will not be spent on software development on Firefox, which is done by Mozilla Corporation. (I'm pretty sure it will fund Mozilla Foundation software developers, though, as well as all of the initiatives they list on the home page.)
So donation money goes to outreach and similar. Which is useful but doesn't fund Firefox.
Someone please correct me if this is wrong.