Download Helper is a Firefox extension . By downloadhelper you can download and convert videos from many sites with minimum effort. Using downloadhelper you can download from XHamster, Youtube, google videos, YouPorn, RedTube, Free18, 3AnimationSexTube, Tube8 and many others. You can also capture image from image gallery.
Downloading link is http://www.downloadhelper.net/install.php. Try it. I hope you will like this.