check for the plugin. if the plugin is missing please install it. The message of missing plugin a message is appeared at the place of content

our read the article this will help to resolve the problem https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues

thank you

try this out bud... go to Start/Run/ type in "regedit" (without the quotes).....

click on: Hkey_localmachine/software/microsoft/windowsNT/Drivers32....... you should have a string named wavemapper.... if you don't, on the left pane where it says drivers32: right click/permissions/advanced .........on all the ones that say Deny instead of Allow, highlight the name and click edit... then under the heading Allow check the full control box ....after checking all those you should have wavemapper as a string name in the right pane along with a bunch of new names as well......go to youtube and give it a shot

Here are a suggestion that can be usefull:

Open Your Control Panel The easiest way to open the Control Panel is to click on "Start" and then click on "Control Panel." Open the Internet Options Double click on "Internet Options" to open that section of the Control Panel. Select the "Advanced" Tab The Advanced Tab is usually on the far-right side of the Internet Options screen. Scroll Down to Multimedia Scroll through the options until you see the section called "Multimedia." Deselect the Play Sounds Option Click to check the option called "Play Sounds in Webpages." This will turn on all sounds in your internet browsers.

Started Firefox, the video on the start page played but kept stopping. After that no sound on any other videos. Will try some of the suggestions when I get home later.