Invisible glass is far better than Windex if there's something stubborn on there, but otherwise PN here has hit the nail on head: DISTILLED WATER is THE "magic" glass cleaner. Wipe down with distilled water, then buff out with clean microfibre towel. Glass will fade to near invisibility. Also don't forget that newer cars interiors are still gassing out and a bunch of the "stuff" the plastics are giving off will condense upon and coat the interior glass with gray hazy stuff. The newer the car, the faster this happens.