With thanks to Skua Sarrasine for having found the first of these.
Symptom: “This is a bug thats only experienced with Firestorm running. Basically, at seemingly random, but very infrequent times, my dual screens will bug out, producing two displays of solid colour, randomly. Sometimes Windows will return saying it recovered from an error code 7 or 3.”
Some research turned up this for error code 7; it suggests setting physX to CPU. And that seems to have solved the issue.
Note also the (apparent) interaction with Chrome.