Lizards, rodents, rabbits, earthworms, fish, mollusks, mice, fruits, berries, snakes, voles, hares, carrions, small birds, eggs and grasshoppers. Depending on the breed the foxes diet will change but most foxes stick to this diet. If a foxes breed requires specific food then they will obviously stick to that diet and ditch their previous one or just stick to the one they were born with. Some foxes have a regular diet like the list above but are picky in a way and change there diet, or just ditch some items in that diet. But that diet could and most likely will pass down to the younger generation. If the adult foxes diet is "unhealthy" then the baby could die if the fox were to be expecting.
Berries by Lukas Riebling from Wikipedia- CC-BY-SA
Fox eating mouse by Us fish and wildlife services found on PublicDomainFiles.com-CC-0
Mollusk by Pezibear found on Pixabay-CC-0
Hooded crow carrion by Zimt2003 found on pixabay-CC0