As we all know animals are terrified of fireworks and this includes most horses so extra care needs to be taken at times when people are more likely to be having firework displays such as Guy Fawkes, New Year, July 4th etc
Forewarned is forearmed, so keep an eye out in the local press etc for advertisements for firework displays in your area. If you know your horse is very scared of fireworks you might consider sedation, your vet will be able to supply Sedalin which will help to keep your horse calm. Also if you know there is to be a firework display near you you can arrange to stay with the horse while it is going on.
Generally we wouldn't advise that you change your horses routine as this will only cause additional stress. If your horse is stabled an extra thick bed well banked around the sides will help prevent injury or casting, remember to check carefully for anything that the horse could injure itself on. If your horse is out at grass make especially sure that fences and gates are in good repair.
It's always worth talking to the organizers of firework displays or parties to warn them that there are horses in the area and to ask them to enusre that the fireworks are set off in the opposite direction to the horses.
Make sure that you have a fire procedure in place and the telephone numbers of the fire brigade and your vet to hand. Also check you have third party liability insurance, if your horse does get out and causes damage you will be held liable for compensation.