On the topic of keeping an extinguisher in your vehicle, when I was involved in the sport up to world rally standard back in the 70s, it was compulsory under race and rally regulations to carry such an item. We always had a powder extinguisher with steel holder bolted to the floor by the navigator's seat in rally cars. You failed scrutineering if you didn't have one. Along with a big red battery/ignition isolation switch for use if and when the car rolled.
No doubt the Group One world rally cars today have even more sophisticated fire retard systems. And for good reason..