Two problems related to front air bag have been reported for the 1999 Volvo S80. The most recently reported issues are listed below.
Air bags deployed while car was in "park" and with no impact.
Power windows would act sporadically, going up or down whenever the button is used. Some time would partially go up or down their its own. Taken vehicle to dealership twice. The 2nd time the mechanic got inside of vehicle & closed door, air bags deployed. Had no indication of why. Dealership having Volvo representative to check vehicle.