I asked a knowledgeable F mechanic why this happens. He says it's the cats that get extremely hot and cause the fires. One of the sacrifices for a high performance engine. There are ways to cool the cats but it's expensive. He suggested the use of platinum material as a coolant. When you see these cars really blow it's usually the fuel fumes that get ignited and explode. The cats are typically below the engine which is also a problem.(more stuff to ignite) With P's the cats are off to each side. On Mercedes they've got several coolers for the cats. So, this problem is something all manufacturers face but others just have better designs to handle the high heat. Sound like not until there is some design changes it's, "burn baby burn."

PS - I don't really think that a fire extinguisher is much of a solution because you're not going to want your car smelling like an old toaster for ever even if you do manage to put one out. Probably best to just let her burn.