this phrase came along because in a gay relationship, the submissives (ones who take it) were usually foxy fluffs, or, in the case of straight relationships, usually the foxy fluff was a girl.
Wolf Furry: i love my foxy!
Fox Furry: <3
Wolf Furry: I love my cockwarmer!
Fox Furry: Oh Murr <3
Wolf furry to other Wolf furry: my Foxy Fluff is the best cockwarmer ever! He is so GOOD...!
Other Wolf Furry: Well so is mine, she is so HELPFUL with it all, too!