The Firetroopers were originally created at the same time as the Imperial Guards who serve a constabulary function on select Core Worlds, and are to provide support to the local fire fighting and search-and-rescue units. They have also been posted on certain worlds with the intent of combating fires in wilderness areas, particularly those started by the Rebellion. The very sight of thier uniforms, along with those of the Imperial Guard, haas become one of the most popular signs that the Emperor has the good of his subjects at heart, at least to Core Worlders.
They are dressed in distinctive red-orange armour and capes which protects them from heat, and carry blaster carbines and pistols in addition to their pack-frame mounted extinguishers (they are Stormtroopers, after all, and are required to uphold the law of the Empire).They are supported by a small number of specially designed droids and vehicles. They are trained to work closely with the Imperial Guard to control the scene of the emergency.
In reality, they usually don't carry fire extiguishers, but rather flame throwers and incendiary grenades. They are used to destroy buildings suspected of housing Rebels (in an urban senario), or forests and jungles that provide sanctuary to Rebel warriors (in a rural senario). For every fire they extinguish, they light another three. One of the smaller branches of the ISTC, combined they only form about two legions. Their two most famous units are the "Smokewalkers", a division ("1st of the 1st Fire") who are tasked to suppress fires in the immediate vicinity of the Imperial Palace and his Majesty's various retreats, and the "Scorching Winds", who have become well known in the Inner and Mid Rim for a series of incendiary missions against rebels, pirates and smugglers. They typically light a forest fire, then walk out of the flames to pick off the survivors.