Joan Rivers: I'm ECSTATIC My Daughter's Dating a Porn King

Joan Rivers couldn't be happier her daughter is dating the god of sex tapes Steve Hirsch -- telling TMZ Live, Melissa Rivers and her new XXX man are a perfect fit ... in more ways than one.

Joan tells us, not only is Steve crazy about Melissa -- "He makes a great living ... and he's Jewish."

But Melissa -- who hooked up with Steve through a friend -- isn't the only one reaping the benefits of her new relationship ... Joan adds, "I'm 78 years old and now I get a discount on lubricant."