Yo,
It should hold a bit in reverse. Ford does not mention this at all in the 96 Bronco-F-Series Workshop Manual (PARTIAL) by FORD
nor the 96 Bronco Owners Guide by Hiller Ford @
http://www.hillerford.com/resource_library/owner_manuals_pdf/1996_owner_manuals_ford/96bronco.pdf
EXCEPT,
"The parking brake is not designed to stop a
moving vehicle, but you can use the parking
brake to stop your vehicle in an emergency if
the normal brakes fail. However, since the
parking brake applies only the rear brakes, the
stopping distance will increase greatly and the
handling of your vehicle will be adversely
affected."
As long as it holds on a slope with engine off & the Bronco facing either uphill or down hill, its good.
The Owners Guide gives info on setting the parking brake.