I believe the ability to add exceptions was removed from the Firefox preferences page. Now you can only remove exceptions from that screen. However, you still have the ability to add an exception using the site information panel. See [[Allow or block media autoplay in Firefox]]. You will only be able to see the permission listed in that panel if the website has tried to play a sound. If that's not something that the website attempts when you load the page, you may not see the permission listed. In that case, if you click the arrow next to the '''Connection Secure''' part, that will move to a different page of the panel. Then you can click the '''More Information''' button at the bottom to open the [[Firefox Page Info window]]. From that window you can press the '''Permissions''' tab and change the '''Autoplay''' permission. Hope this helps.