Terry has heard that if you want to stop drafts, you need to take the trim off from around the inside of windows and seal that gap between the drywall and the window frame behind the trim. He suggests simply covering this gap with aluminum duct tape.
That is a great idea Terry. Aluminum duct tape is one of the sturdiest and longest lasting of tapes you can buy to seal air gaps. If the gap is less that 3/8 inch, you could caulk it shut. If it is more, you could use foam in a can over the fiberglass, but don't try to shoot the entire cavity with foam -- the kinds you can buy on the retail shelves expand too much for that and may jam your window shut. But Terry's aluminum duct tape solution is considered a good alternative by those who study such things.