Why are firefighters first on scene?

The reason firefighters are first on scene is because of the mandate set forward by the National Fire Protection Association. A response time of 4 min is the target, where as with the Ambulance, the target is 6 to 10 min.

Depending on the city, there are usually more fire halls than ambulance stations, which also increases the chances of a faster response time.

when you say first on scene im guessing that you mean when you call 911 for an ambulance why do the firefighters come to.

The simple answer to that question is that depending on where you live:

if you live in the city, there may be a fire station close to where you live that has Firefighter/emts on station, and they respond on medical calls to get things started until the ambulance can get there

if you live in the country the fire dept is sent for lifting assistance and to get things started until the ambulance can get there (may take upto 20 min around where I live)