YouTube is one of the biggest video sharing website in the world.If you download YouTube videos from third party tools then it will give a video file with .flv extension. Many media players don’t support this extension and that’s you have to convert file or upgrade media player with suitable codec.To overcome the problem of downloading videos, you can use “Download YouTube As MP4”- a Firefox plugin, which helps you download videos in MP4 format. Almost all media players support videos with MP4 extension.

Read more/Download : visit https://addons.mozilla.org/en-US/firefox/addon/11869