Firework sounds are classified as Ambient/Environment noise. This should be placed under a different controller, because Fireworks aren't really ambient or part of the environment.
Maybe a new slider made just for entity sounds?
MC-63638
Firework sound control
Resolved
Incomplete
0
Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.