Firemouths just 'Flare n scare' just like barking dogs, and they successfully keep away most mid sized moderately aggressive cichlids this way, they dont indulge in serious fights though, atleats in my experience they have hardly injured any fish(even small characins). But if you keep them with large predatory fishes like big gars, bichirs, red tail catfishes(and alike), even large knife fish(exceeding 18"), jumbo cichlids, etc., then, most likely they'll disappear someday....