1996 Geo Metro window will not stay on track

The window has fallen out of the track of the door regulator. The car was sold to my wife with the driver font door handle removed. I removed, lubricated and replaced the door regulator. It works fine. The problem is the window does not stay in the track. I know very little about how a regulator works. I assume the track silides along the bottom of the window as it is raised or lowered. There is not a rubber gasket in the glass track of the regulator or on the bottom of the window itself.