I've never heard someone in Scotland say firefighter. Fireman/Firewoman should be acceptable answers.
Firefigher is now the official lowest rank in the Scottish Fire & Rescue Service, so calling any old person in uniform a firefighter might be disrespecting them if they're of a higher rank (though I can't imagine any would take offence). As I said though, I've never heard anyone say "firefighter" though the usage does seem to be increasing (https://books.google.com/ngrams/graph?content=fireman%2Cfirefighter&year_start=1800&year_end=2019&corpus=29&smoothing=3&direct_url=t1%3B%2Cfireman%3B%2Cc0%3B.t1%3B%2Cfirefighter%3B%2Cc0)
People say police officer when rank is unknown, but it's rare. For decades there was a separate designation "Woman Police Constable/Sergeant" for females but that was discontinued about twenty years ago.
That's the first I've ever heard "letter carrier" I'm not sure of official designations, but folk just say "postie" 90% of the time.