EXTERNAL TEMPERATURE WAS ~22DEGREES F, HAD REAR WINDOW DEFROSTER AND HEATED DRIVER SEAT TURNED ON. FRONT DEFROSTER WAS ON AND SET TO HIGHEST TEMPERATURE. WHILE DRIVING AT 25 MPH, MY SON AND I NOTICED A BURNING SMELL. HE WAS SEATED IN A BOOSTER, REAR SEAT, PASSENGER SIDE. HE ADVISED THAT HE COULD HEAR SOMETHING BEHIND HIM MAKING NOISE. I LOOKED BACK AND OBSERVED SMOKE COMING FROM BEHIND THE REAR PASSENGER HEADREST, WHERE MY SON WAS SEATED. I LOOKED FORWARD TO FIND A SPOT TO PULL OVER AND THEN HEARD A LOUD BANG. LOOKING BACK I SAW THE REAR WINDOW WAS SHATTERED ON THE PASSENGER SIDE. IT IS A SLIDING REAR WINDOW WITH THREE SECTIONS, ONLY THE PASSENGER SECTION,DIRECTLY BEHIND MY SON WAS SHATTERED. THE GLASS REMAINED IN PLACE, BUT SHATTERED. I QUICKLY PULLED OVER, SHUT OFF THE TRUCK AND REMOVED MY SON. FROM THE OUTSIDE I CAN SEE THE PLASTIC LOWER CORNER MELTED WHERE THE PASSENGER GLASS MEETS THE CENTER GLASS SECTION. THE RUBBER SEAL/MOLDING WAS SMOKING AND HAD MELTED AND DRIPPED DOWN THE BACK OF THE TRUCK CAB, BETWEEN THE CAB AND THE TRUCK BED/BOX. INSIDE THERE IS A STRONG ODOR OF BURNT RUBBER OR PLASTIC. *TR