It's been claimed on these forums that he used a continental grip for both backhand and forehand. Some of those people seem to be claiming that the continental is a good choice of grip for a one handed backhand.Edberg always used an eastern bh grip on his topsin bh.
I don't know for sure what he used to use. The old footage I've seen it's hard to tell. Anyway, it makes more sense to me that he didn't, but it seems to have legs on this forum, so I don't know.