Assuming it's an engine compartment fire, I'd take my HalGuard extinguisher and spray it into the passenger side vent. Not sure where the fan is located, but the blades look open enough for the spray to get into the engine compartment when the fan isn't running. At least that's my plan. For a fire elsewhere, I'd shoot it at the source.
I love my car, but if the fire looks too dangerous, I'm not risking my skin and my life to get underneath, or start pulling carpet from the trunk or frunk.
