current dog is trained for gun shots but don't like firework and thunderstorm. the old vizsla was completely indifferent against firework burning 2 meter beside of him.
when I notice he fear firework- first sylvester night when he was 7 months old - start again with shot training with a 6 mm blank firing pistol.first at long distance then coming closer while he was hold by his beloved mistres all the time.this happen over weeks with maybe 3 - 6 shots a day until we were seeing it was good now.
there must be a difference in the noice! a 12 ga shotgun at close range is no problem but firework at 1 km makes him still nervous.
I recommend allways the small 6 mm starting pistols for dog training. its a real shot but not to loud to make the ears ringing. start from a dictance then coming closer and the dog must be with someone he real trust.not to tell him that everything is fine, he knows something happen and its not exactly fine.
but there is someone he trust and he see than what make's bang nothing bad happen. and than the good things in live must come for a dog. it makes bang and a moment later he find game and can retrive so the noise will be connected with things that make fun.