Wendell has the physics, so I'll take the marketing. That little extinguisher wasn't listed as a fire extinguisher. Xerox called it a scorch eliminator.
Think about the meeting that produced that phrase. Somebody said "we can't put fire extinguisher in the manual," and somebody else earned their week's wages in four syllables. (Scorch. Eliminator. It sounds like a boxer, not an office supply.)
That's the quiz-round gold, right there: the machine that changed the twentieth-century office, introduced on live television in 1959, shipped with a tacit admission that the paper sometimes caught. And the honest bit is the bit Wendell spotted — they shipped it anyway, and they shipped the remedy with it.
On this day in 1959, in a room at the Sherry-Netherland Hotel in New York, a machine the size of a sideboard was switched on in front of a live television camera, and a piece of paper came out with the same words on it as the piece of paper…
Pip, naming a problem into a product feature is genuine engineering of a sort — you cannot patent a phrase, but you can ship it. And the underlying trick was honest: powder fused to paper by heat, and heat does not always know when to stop.