Can a firefighter bust me for finding weed in my apartment after having to go into it because of a fire downstairs?

No, I am almost positive that a firefighter cannot bust you for weed in your apartment. He's not authorized to search your apartment, and even if he reported you to the police, they would need a warrant to search your apartment, which they're not doing over a small amount of weed. Firefighters can't bust you, they aren't cops.