WARNING: This page is about a different car, the 2004 Mercury Monterey and 2004 Ford Freestar. However, it is still accessible from the selected car via links, so may be relevant.
Release the J-clip.
Fig 1: Releasing J-Clip
Courtesy of FORD MOTOR CO.
Reach up in the seat back and pinch the end of the head restraint sleeves and remove.