Ultimate YouTube Downloader is a little Firefox add-on to download YouTube videos as FLV, MP4 and 3GP.
The best side of this add-on is its small placement below the video. It does not take larger area. Install this add-on from here. You need to check the Let me install this experimental add-on option.
After installing the add-on, restart the Firefox and you will notice the “Download” option below the video. You don’t need to use any extra tool, simply select the format from the drop-down menu and click on the “here” link.
Link : Ultimate YouTube Downloader