Do I understand correctly that the parent nonprofit Foundation can decide to use some of its donor money to fund its for-profit Corporation (with the same tax treatment as any other investment, and of the corporation’s profits before they’re returned to the Foundation)? But donors can’t direct their gifts to that use if the donors still intend to deduct them as charitable donations?

And thus I guess Foundation has to do a good amount of conventional non-profitty stuff like “education and advocacy,” otherwise it would just be a flimsy facade for what’s substantially a for-profit endeavor?

Why is the browser arm organized as a for-profit at all?

It's the other way around, Mozilla Corporation is profitable and those profits go directly to the Mozilla Foundation which owns 100% of it.

This idea that Mozilla doesn't have enough money to fund Firefox is just wrong, Firefox development is perfectly sustainable, it earns more money than it spends. If you want to give money to the Mozilla Corporation instead of the foundation, you do the same thing as with any company: you purchase products from them (such as their VPN or MDN Plus, both of which are owned by the corporation).

> Why is the browser arm organized as a for-profit at all?

So that they can make business deals with the likes of Google, which they wouldn't be able to do as a non-profit.

Edit: I really wish there was a single thread about Mozilla here that doesn't devolve into this being like 80% of the comments. Maybe one day.