Strictly speaking, Apple provides nothing to you for free even if you develop and intend to release a free App.
I believe organizations like Mozilla qualify for a $0 developer fee.
They do, but then they wouldn't be distributing on the App Store anymore. Nevermind the fact that a business shouldn't have to be a nonprofit to feasibly ship FOSS software.
Firefox and Firefox Focus plus whatever other apps they have are on the iOS and iPadOS stores at least, maybe others.