SMOKE SUDDENLY APPEARED IN CAR INTERIOR WHILE DRIVING ON A HIGHWAY. I PULLED OVER. SMOKE BECAME MORE INTENSE. OPENED SUNROOF. FLAMES OBSERVED IN HEADLINER/DOOR JAMB ABOVE DRIVER'S SIDE. FIRE EXTINGUISHED BY FIRE DEPARTMENT BUT NOT BEFORE EXTENSIVE DAMAGE TO THE HEADLINER/INTERIOR AROUND THE DRIVER'S SIDE. CAR INOPERABLE.