I also use Firefox and have no sound - in fact, I didn't realise there was meant to be any! I'm guessing here, but I think you may not have the Java Plug-in installed. In Firefox, go to Tools -> Add-ons -> Plugins and see whether Java is shown in the list. If not, go to Java.com and download and install the appropriate version for your operating system. It should then appear in the list, but you may need to enable it.
No sound whilst using Firefox

its no fun to play without the sounds esp. when 1 minute games. My sound has been off for a couple weeks. Does anybody know of a better website to use?
I'm new here.
I also use Firefox and have no sound when making moves.
I see the last post here was 5 months here.
Was there a fix or is this still an issue.
Can someone help me please with a problem which has been bothering me for a while and stopping me playing much on chess.com during that period.
My main browser is Firefox. Always up-to-date. Whilst playing games using Firefox, I cannot hear the pieces being moved, neither my own pieces nor my opponent's. This is a significant disadvantage, particularly when playing bullet or blitz.
The problem does not manifest when using other browsers.
Any ideas out there?