I was not expecting to be considering the acquisition of and benefits of salt in a world covered in apocalyptic fog but here I am! Kind of an awesome idea in its own right, I could see just the ideas in the Salt "Rumors and Rules" section revised into something even more substantial.
The adventure itself has a really fantastic little premise and is easy to imagine as some Folk Horror situation that just hasn't had a movie made about it yet. Aces for that.
As it is with FatherFog I think the Fire Demon as a source of strife and a creature to pin an adventure on doesn't strike me as explicitly fairy tale, folklore, or myth in quite the way that first comes to mind BUT I really don't think that's a material issue given how strong this concept is. In terms of the theme of the jam that's been used to great effect.
Echoing some others I think the visual presentation is all that needs revision here.