On a flight with Air Transat, passengers were informed that for use in the in-flight entertainment system, only earbud style earphones were permitted.
I ignored this and used my on-ear style earphones (I hate earbud style earphones), and the cabin crew did not tell me to take them off. I could still clearly hear announcements, and in any case, those announcements could be transmitted through the audio of the in-flight entertainment system, so being unable to hear important ambient sounds does not seem a reasonable motivation.
Why would only earbud style earphones be permitted? Is this rule common and commonly enforced?