You won't reliably sex fire mouths until they are fully matured. Even then it can be difficult unless the pair are side by side.
People say males are better colours with longer fins but this can be unreliable.
Males tend to be bigger and a little more impressive looking but only once maturity is reached.
Other than venting the fish,it's just guesswork for now.
Yours looks about 3" long and from 2.5" sexual differences start to become apparent. USUALLY males get longer fin extensions and have a longer snout with bigger mouth and squarer more muscular looking body. Females tend to be smaller and stouter in the abdominal area with shorter face.