Saw this video yesterday. You can barely perceive a fire, except from what might have been lit by his exhaust on that hill.
Just last week a guy in southern France did the deed flying a converted Grumman Tracker. He'd been firefighting for six years and previously flown Mirages for over a decade, so I doubt his skills are in doubt. It's just that the terrain isn't always friendly, the convective turbulence must be brutal, and visibility sometimes pretty minimal. And on bad days they must just get tired. Dangerous business.