One thing that is not mentioned is if car is a 2-door or a 4-door (or wagon) - which makes a difference.
The 4-door (and wagon) door glass is surrounded by a metal frame. Both front doors have a window run channel that goes into the metal frame and glass slides in front/rear & top part of glass. Both rear doors, the run channel is for front and top edge of door glass. the rear edge of rear door glass has a slide.
Both front and rear door glasses have an attachment to window regulator on bottom edge of glass.
If a door glass is loose, we need a bit more information as to up/down, front/rear or inside/outside movement (or combination of the above), to help point as to what to look for.
The window run channel is one really long piece. This is a picture of it on my '86 Fifth Ave, which is broken. I pulled it out a portion to get a good picture of it and need to find a replacement.
FMJ 2-door cars are a bit different sense there is no frame around the door glass.
BudW