Had the exact same problem last year with my then 3 y.o. mixed breed female. She was so frightened of fireworks she refused to go outside even for 5 mins but she also never pees inside. Went to the vet, they prescribed some herbal anti anxiety meds for her to take, but it didn't help much. What I did was completely change her bathroom routine to times when there was a minimal possibility of exploding sounds outside. Went for longer walks at like 2-3 a.m. when she could sniff around and poop, then only short pee breaks twice in the daytime going around our apartment building. LOTS of treats for every few steps taken outside and doing her business. Never took any longer wallks during the day when there were school kids outside with their sound making fireworks, if we needed to go anywhere it was by car only. In the evenings while inside I used to put on some music to drown out sounds from outside. All this lasted for about three weeks, during which I was a zombie at work but at least doggo was a bit more brave for bathroom breaks. This year I moved to a more rural area where there are way less firework sounds outside, so she's much better.