Chances are your sound is muted for Firefox only. Did you take a look at the [[What to do if Firefox won't play any sounds]] support article? If not please do so, and follow related / referenced articles provided there.

Hi ! This problem is caused by the latest Windows update. Would you please take a look at this bug report : https://bugzilla.mozilla.org/show_bug.cgi?id=1426719 And also : https://www.onmsft.com/news/windows-10-insider-build-17063-breaks-audio-in-firefox Maybe you'd like to post on the Microsoft support forum and ask them when this will be fixed : https://answers.microsoft.com/windows