Front airbags are standard equipment for sure.... it's been that way for quite a few years now. But I'm not sure of the exact year that they became standard equipment.
When the technology was new, it was common to see just a driver's side airbag... no passenger airbag at all.
Airbags became standard on the 4Runner in 1996. It has both a driver and passenger. I don't think any 4Runner has only had one airbag. It was two or none.