Finbar wrote:

I think I can see how this would happen with the canopy open, and the
sunlight hitting it from "inside," reflecting off the canopy surface
onto the focal point of the almost-parabolic canopy. I'm still
holding onto the idea, though, that this can't happen in flight
because the sun can't hit the canopy from the inside. The thought of
an in-flight cockpit fire is really not comforting. Has anyone had
solar/canopy - related charring happen in flight?

I completely agree, focusing solar light can only occur by reflection,
by transmission, as the canopy has parallel inner and outer surfaces, it
cannot change the direction of light rays, only slightly offset them.
Hey, this is just why we can see through it as if it were not there !