Several embodiments of a firewall sleeve system for preventing the propagation of fire along a cable, wire, line, pipe, conduit, and the like are disclosed. The firewall sleeve systems comprise a front/male housing with a first flange area and a rear/female housing with a rear/female flange area. Preferably, the rear/female housing and front/male housing are structured and arranged so that their flange areas do not have to be anchored into or cantilevered from a structural element. Moreover, the rear/female housing is frictionally and securely attached to the front/male housing so that the flange areas of each housing are on opposite sides of the structural element and, furthermore, are flush or substantially flush with their corresponding sides of the structural element. Also disclosed are methods of preventing the propagation of fire along cables, wires, lines, pipes, conduits and the like.