A few days back I had reviewed a very cool free software called Webshot that can capture whole web page in one single image. Today I found a Firefox plugin that can do the same, and much more.
Screengrab is a free Firefox plugin that can capture entire webpage in a single image. On top of that, it can even take screenshot of your entire window, only a particular selection, and even take screenshot of any particular frame. Screengrab can save the captured image directly as a file, or place that on clipboard. Then, you can use some good free image editor to edit it further.
Screengrab makes it very easy to take screenshots of webpages by directly integrating in the Firefox. It is totally free, and extremely easy to use. If you are looking for some other full fledged image capturing software, you can try Gadwin Printscreen.