There are many extensions to do the same in Mozilla firefox, so here is one for google chrome fans called Webpage Screenshot.

Go to the extensions page in chrome and click install :

https://chrome.google.com/extensions...hgiakhnjcddpki

To take a screenshot click on the webpage screenshot icon on the google chrome toolbar. There are 3 options to take a screen shot.

Visible Area Screenshot
Entire Webpage
Resized Window

The options are self explanatory. To take the screenshot of the entire webpage, both that is visible and the non-visible area, choose the entire webpage option. To take a screenshot of the visible area choose the visible area screenshot. It gives the screenshot the same way as it is seen on the screen, ie if the browser is minimized then the screen shot will also reflect the change in size.

If you want the image to be of specific size, then you can choose resized windows and then choose a pre-defined size or choose an area in terms of pixels.