Firefighter missions involve driving a Fire Truck and extinguishing fires across the city. To start, enter a Fire Truck and press the designated button. You'll be given a location with a burning vehicle or building, and you'll need to use the water cannon to put out the flames. Completing levels of Firefighter missions will make Tommy fireproof, a very useful ability in later missions.
These missions require precise aiming with the water cannon and quick navigation. The Fire Truck is slow but durable. Reaching level 12 will make Tommy immune to fire damage, which can be a lifesaver in certain combat situations and allows you to walk through flames without taking damage. This is a highly recommended side activity.