1) Person who generally fights fires, saves people from fires, exhibits fire safety at local schools, etc. Almost always in prime physical condition as to do their extremely dangerous job well. Also stereotypically male, although there are indeed female firefighters.
2) Post-9/11 adverb used to modify another descriptive adjective. Generally used to impart positive descriptive terms, can be used as an all-purpose intensifier.
1) "Jeff is a firefighter. He's heroic, brave, and hot as all fucking get out."
2) "Ooh, lookie lookie! That boy over there! ... Firefighter cute, girls. If only Jacob could be that hot. He'd probably be able to satisfy me, what with all those well-defined muscles, pumping maddeningly into my love canal ... Oh, damn. Now I have a wideon." OR "Dammit, Merthedil, you're being firefighter obscene!"