A new extension is added to my favorite Firefox extensions, Screengrab. Screengrab lets you save anything that is visible in the browser window as an image. You can either save the page or save the selection to clipboard, so that you can paste it into documents or emails. You can also save the entire scrollable webpage as an image. Try it!
Screegrab Homepage: http://www.screengrab.org/
Below is the image I have screengrabbed with this extension: