Open Firefox and play contents that should play sound: an HTML5 video with audio track in this Firefox videos page, a Flash sound, etc.

   Click the volume icon in the Windows task bar.
   Make sure the Mute checkbox is not checked and slider is not at the bottom. 

Check your audio device

Make sure that the audio device (such as speakers or headphones) are turned on and connected to the computer properly. Other solutions

Check out whether other applications on your computer can play sounds. If they can't:

   Follow Microsoft's No sound in Windows tutorial. 

If Firefox is the only application that you can't hear sound in:

   Try the solutions in Fix common audio and video issues. 

Did this fix your problems? Please report back to us!

Thank you.

Did you check the media player to make sure that the sound isn't muted?

See also:

• https://support.mozilla.org/kb/fix-common-audio-and-video-issues
• http://kb.mozillazine.org/Video_or_audio_does_not_play

Type about:addons<Enter> in the address bar to open your Add-ons Manager. Hot key; <Control>(Mac:<Command>)<Shift> A)

On the left side of the page, select Plugins. Make sure the ones you want to use are set to Ask or Allow.

Go to the web page. Once the page is loading, mouse to the address bar and Left click the icon. A window for displaying site information should come up. Select More Information. Now select Permissions. In the menu, find the plugin, and set it to Never or Ask. This action will only effect that one site.