In my prior car (Mercedes CLK 500), I had the factory fire extinguisher on a bracket attached to the drivers seat. i remember it was around $300 for the European bracket and extinguisher to be shipped to me from The Netherlands, since it wasn't available in the US. A couple of years ago, as I'm getting on the freeway near my house. I see a small brushfire has started on the on-ramp. I blocked the traffic, grabbed the extinguisher and put the fire out....then paid the stupid $300 again for another extinguisher. Anyway, I couldn't figure out where I could mount one within easy reach from the driver in my Model S, so I mounted one in the trunk, instead. This is the one that fits in thats space. I spray-painted it black first...
I'm guessing it's for when he goes tailgating at the next big game and pops open the frunk that'll contain the barbecue...
I've always had an extinguisher in my cars. I'm just pointing out a place to mount one for like-minded people. Better to have one and not need it, than vise-versa.