Take Screenshots of Entire WebSites in FireFox (Addon) with ScreenGrab
Taking screenshots of entire websites wasn’t this much easier for firefox users. Instead of going to third party websites that let you take screenshots of entire webpages, you can use ScreenGrab — a great firefox addon which does the job through right-click context menu.

(Don’t worry, I’ve just stripped some addons in the screenshot to give you a clear view)
It’s very easy, After installing the addon, visit the website, right click, click on ScreenGrab! and you’ll see two options, save and copy. If you click save, it will save the entire website screenshot into a image file to your computer. And if you choose copy, it will copy the screenshot of the website into your clipboard so you can paste it wherever you want to. It works great with firefox version 2.0 to 3.0 etc.