All local fire fighters here are paid. The boot collections are for groups needing donations as Cookie said. My town has been building nice new fire houses, there's one up the road from me not even two years old, maybe I should take a pic.
Typically Volunteer Fighters are for areas which can't afford a paid force and the population is smaller which means less fires. And, as mentioned, the guys do for the adrenaline rush and also because they like to volunteer for community service.