Use the Video DownloadHelper to download video in Linux

There are more than one method to download a video in Linux, but Video DownloadHelper is the easiest way to do it.
DownloadHelper is best installed from he Mozilla Add-ons site. Go there and just click on the Add to Firefox button and follow the instructions.
When the DownloadHelper is installed, there is its icon () in Firefox Navigation Toolbar.
If we want to download a video, we just open the site. Video DownloadHelper will activate and we just need to click the icon, then choose the video type to download (.flv, .avi, .mp4).