I checked the airline fleet site. I stand quite corrected:
http://www.geocities.com/~aeromoe/fleets/fedex.html

FedEx has 25 active A-310's, and 28 A-300's. They appear to have quite a number of additional 310 and 300's "on order"; which I suspect means they are being bought from another party and converted. Based upon the registration data, many of the 310's were orginally German domiciled, and the 300's from France. Actual previous owner is not disclosed, although some of the 310's were American owned, with a "PA" (PanAm?) suffix.