That was simply AWESOME!
Don't worry he can't fire you, if he does attempt to victimise you, you have your motive right there! All your colleagues witnessed you stand up to him! They will be your witnesses in unfair dismissal suit against him and the school if he dares!
He might be a bully, but I don't think he is stupid - so you will still have your job. Do let us know how it goes!
A loving Mum.
Daily I worry for the safety of my young sons - but worry achieves nothing! So I pray for their safety!