DownloadHelper

http://www.downloadhelper.net/

DownloadHelper is also a free Firefox extension for downloading and converting videos from many sites with minimum effort.

Using DownloadHelper, you can easily save videos from most of the popular video sites. 

It is also possible to capture all the images from a gallery in a single operation.

Note that DownloadHelper does not break any real protection implemented on the sites. It just give an easier access to clear content that will be downloaded by your browser anyway. Unless exceptions, downloaded videos must be kept on your disk for personal use and not shown on other Web sites.