If you are an addict to download every single YouTube video you watched, this add-on, Easy YouTube Video Downloader for Mozilla Firefox is suitable for you. With just a single click on the direct download link you can save the YouTube video for FLV, 3GP and MP4 video quality. The current release version 1.6 works with Mozilla Firefox from version 2.0 to 3.5.* and this add-on works great for me in Windows. Please give it a try on Linux and Mac version of Mozilla Firefox. Looking forward to your feedback.
Source: Easy YouTube Video Downloader