Final answer:
Fire extinguishers containing chlorofluorocarbons (CFCs) were made obsolete due to their harmful impact on the ozone layer, leading to worldwide phase-out efforts.
Step-by-step explanation:
The type of extinguishers that were made obsolete because of their ozone-depleting potential were those containing chlorofluorocarbons (CFCs). CFCs, often used as aerosol propellants and refrigerants, played a significant role in the depletion of the ozone layer in the stratosphere. Through photodissociation, CFC molecules release chlorine atoms that catalyze the destruction of ozone molecules, leading to the formation of the 'ozone hole.' The Montreal Protocol of 1989 was a major step in phasing out the use of CFCs and other ozone-depleting substances by replacing them with less harmful alternatives.