"[Pulls Faustus by the leg, and pulls it away.]..."See in text(Scene 10)
Trying to wake Faustus, the Horse-courser shakes Faustus's leg and is then horrified when the entire leg comes off. This can be read as a cruel joke on the Horse-courser or as a symbol of Faustus's decay. He is not sleeping, and now his body is falling apart. Faustus's damnation now manifests itself in his physical being.
"Glass windows" in this context refers to spectacles or glasses. Glasses symbolically represent learning and wealth as they were expensive to buy and generally only necessary for reading.
