^^^ This. It's called outgassing, and it comes from plastics and other man made materials. Nothing can really be done to speed up the process, except maybe leaving the car in direct sunlight with the windows open. Still, some cars take forever to completely finish the process. Sucks big time. I've heard that some folks have had success by placing an ozone generator in their cars overnight for several days/weeks. I've never tried that, so I can't say one way or the other.
Just the plasticizers in the interior finishes wearing off...perfectly normal for a new car. It takes about a year or two before the accumulation in the window becomes more "normal" ;) P.S. The more you park the car in the sun and heat, the more you will experience this. If you get it clean and garage the car, you will not experience it much. They sell special window cleaners at the auto parts store for dealing with this...they are ammonia free to keep from attacking the dashboard materials. Look in the detailing section. I've learned that it is best to put on a slight mist, and rub straight up and down to keep the streaks at a minimum.
My previous car was a 1999 Pontiac Sunfire GT (which I bought new off the lot). The poor car lived in the sun, and never stopped making haze on the inside...it had the new car smell until about 2006 or so
It did slow down a bit after owning it for two years, and I'm a nonsmoker.
Or you could say the Mustang is nicely sound and air tight. I think this is why the windows come down partially when opened.
