Someone posted this a while back:

Remove the rear view mirror [it pops off at the base].
Remove the 3 screws holding the mirror plate to the header.
Pop the visor out of the plastic support.
Remove the plastic support with a phillips screwdriver.
Look for the hole about an inch or two from the pivot, there is a screw in
that hole. Remove it.
From the middle, drop each trim piece.
Look on the inner edge of the visor pivot for a screw. Tighten it. That will
tighten the ball in the
socket and the visor will stay up.