Does fox fur become pure through tanning, is it permissible to use it in clothing and other items, and is it lawful to buy, sell, and trade it?

The skin of a fox is impure (najis), because it is a beast of prey. There is a prohibition against eating any fanged beast of prey, and against the skins of beasts of prey in general, and specifically against the skins of tigers, and that the angels do not accompany a group that includes a tiger skin. This is due to the adornment and pride involved in their use.