No requirement for an extinguisher, but a welcome addition in case of.
However if you come across a vehicle beside or on the road, where there is an immediate requirment for emergency aid, then the obligation is to stop, check and offer aid, unless the occupants declare themselves competant, or say that help is already on the way. Evidence of failing to stop in such circustances can render the would-be fail to stoppee to a fine, almost as serious as failing to stop for an accident in the first place.
Interesting to note that if a Police officer (from Guéret say) should come across an accident outside the town, then he will stop, tender first aid, offer comfort, and control traffic until the arrival of a gendarme who will deal with the accident. If a Gendarme comes across an accident in the town, he will stop, render first aid, offer comfort, and control traffic until arrival of the police who will deal with the accident. The law is the same, but the competancy changes at the town limits. THey have the same powers, but that's where it ends.