The YouTube Downloader and Converter is yet another Firefox add-on that lets you download videos from YouTube in any format that you wish.
Here is more about this extension from the developers:
YouTube Downloader and Converter is a firefox add-on can generate a download button on YouTube video page, It can allows use download YouTube video with different video quality: 1080P,720P,480P etc. Further more, user can use free client program convert downloaded video to other formats.
Supports all available formats (MP4, FLV, WebM, 3GP) for any video quality.
How it works – It simply adds a “Download” button which populates a list with all the available videos to download.
To download a video – whenever you are on a video page, you will see the “Download” button with a round red icon in it, click that button to populate the list of all available formats to download, click the desired format, save to your hard drive and that’s it!
Give it a shot and let me know what you think in the comments. You can pick up this add-on at the Firefox Add-ons website.