If it was a laptop battery fire, a fire extinguisher might not do anything. Those things are pretty vigorous.
My "plan" for that is to switch on the autopilot, altitude hold, pull back the power to idle, full flap, and at the instant of the stall warner going off open the door and chuck the thing out.
At ~ 60kt it should work.
Unlikely to have been a fuel fire - the only fuel going into the cockpit should be the fuel pressure gauge, maybe. That leaves an electrical fire, or a human-caused one like a fag being dropped.
Re a fuel fire, this makes a powerful case for using hermetically sealed switches throughout the cockpit. They did this after Apollo 1 for exactly that reason, and it more or less happens on upmarket planes, e.g. a TBM uses mil-spec sealed switches. But switches within avionics are generally open. It is easy to make the PTT switch sealed. Not that I think this was a fuel fire.
But yes I would not buy a single door aircraft either...