Screengrab Addon for Firefox 2
Note: the only link in this post is now broken. Left as originally published.
What it does is to save a website as an image. Everything is saved in the process which means that the image can become really big. I love it because I think it is so much easier and better to save a website as an image instead of saving the htm files with all the other elements using Save Page As.
From http://www.ghacks.net