If you ever have the need to take a screen shot of an entire webpage (not just the visible portion), then the Page Saver Firefox plugin from Pearl Crescent is just what you need.

This plugin installs a button on your toolbar which can take a screen shot of the entire webpage or just the visible portion and stores it as a single graphic.
Download it here: [http://pearlcrescent.com/products/pagesaver/]

Note: Be sure to use this responsibility. This is not intended to be used as a means to distribute copyrighted material.