I think that Hermione calling Firenze a horse was just a way to cover up how she feels. She's always saying Trelawny is a phoney. She also said that real seers are really rare. She was probably kicking herself becuse there was finally a real seer and she wasnt in his class to learn about it. So she has a little animosity
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Now that Umbridge is gone, and Dumbledore is back, that means Trelawny will have her job back, right? What does that mean for Firenze? Because he can't go back to the centaurs now, can he? I mean, will he stay at Hogwarts and teach another subject maybe, or go find another group of centaurs?