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Go to a marine or boat shop and get some "Woody's Wax" for fiberglass. Either that, or some guys just repaint the hardtop with rattle cans/spray paint. It's cheap and lasts a few months.
Stoner has a vinyl repair spray , lasts so far 3 weeks lot's of sun and a few washes doesn't drip gives it a nice black luster similiar to a tire shine and wipes off the paint and windows quite easily 5 bucks a can bought it at schucks....
It's not bare fiberglass - the fiberglass is white, and smooth. All '78-96 Bronco tops were factory painted with FLAT SPATTER paint. They aren't supposed to shine.
Trade secret!
You can prime the surface of the removable top with regular latex primer (roll on) household exterior type; than paint the top with your choice of color at least 2 coats (again your household exterior type) followed by one or two coats of clear.
The top will look brand new even after the Bronco does not.
Good for life of the truck if done right.