Fireworms are carnivores that eat corals, snails, crabs, starfish or other worms,
And fireworms have built-in traps that effectively catch prey wherever they find it. The front end of the worm looks rounded and harmless, like an earthworm. But when a fireworm sees something to eat, it rapidly everts its throat, which bears two sharp jaws inside. These jaws seize the prey, and then the worm retracts its throat, pulling the food inside.
Got this from some site. So fireworms are bad in all cases and will eat your fish, inverts, and corals.