If you're talking about a fine layer of weirdness on the inside of the windows, then here's what it probably is:
They plastic in the dash and upper door panels breaks down and vents fumes into the cabin. Those fumes hit the windows and stick. I don't know of any way to stop them, except maybe a dashmat. The coating is a b!tch to get off, no matter what kind of cleaner you use. I usually try a dry paper towel first to remove as much of the residue as I can, then move on to regular cleaners. Good luck with it!
