You can download YouTube videos for offline reference. But YouTube is not providing this facility. Most users are downloading these videos with some software or online converting websites. But here you can see how to download YouTube videos in a single click with the help of a Firefox add-on.
“1-Click YouTube Video Download” is a Firefox add-on for downloading videos directly. No need to go to any other sites to download /convert the video. You can download these videos in deferent formats like FLV, MP4 and 3GP. No need to depend flv converter to convert it to your mobile 3GP format or MP4 formats. You can also convert HD videos directly.
Install this firefox plugin, After that You can see a download link below the video. In a single click it will start download.
Plugin Download link : https://addons.mozilla.org/en-US/firefox/addon/13990