Save As Image is an extension for Firefox that offers the possibility of capturing a complete Web page in one image in JPG or PNG. You may not only determine the file format, but also its compression, so you get a better relationship size and quality.

The difference between Save As Image and a program to do screen shots resides in that this extension takes an image of the complete page (the complete one) even when part of it is not viewed due to its size.

Anyway, Save As Image includes a personalized way of capturing the image so you take just the part you are interested in.