I keep my fire extinguisher in the cab, with me. The first commercial vehicle I drove, the fire extinguisher was mounted on the side of the B-pillar. Later, due to complaints about height, it was mounted low in the middle, between the front seats. Still later, in front of the base of the driver seat. After I changed jobs, I was told to equip my vehicle. A fire extinguisher was required, but not supplied. I mounted it on the B-pillar behind my left arm, as seated.
In the Fiero, the fire extinguisher sits on the passenger side, between the seat and the door sill.