Firefox will not play sound if some of the plugins are disabled.
You need to be sure that the browser handles the file well when you load it.
Case: My downloaded files are playing, but with no sound on my windows 7 installed PC, I don’t know what is the reason, Any help?
The next step is to select the output format from the top left corner drop down menu, in this case we select MOV.
To sort the sound issue on Windows, you need to make sure that you have the Quick Time player recommended settings in place.
In case the codec bundle comes with an installer just run the installation assistant and, if requested, reboot your computer.
If no installer is available then you should know that any codec you may need should be placed inside the folder /Library/Quick Time.
You can change the download action every time the browser opens the media.