This FireFox add-on makes it very easy to download YouTube videos. All you have to do is navigate to a YouTube video and then click the Video DownloadHelper icon at the top right of the FireFox browser. Then all you need to do is select the file type and size you want the video to be. It is so quick and once it is done you can double-click your downloaded file and it will open with whatever you use to watch videos offline! Easy as pie!