Better idea: run Firefox with the FireShot add-on so that you can get the whole page instead of just the visible portion of it.
Then you go into XnView ,import the clipboard (Ctrl+Shift+V), and save it as whatever filetype you want. XnView also has cropping functions so you only need to keep the part you want anyways.
I have mine set so that as soon as I take a screenshot, it automatically opens in XnView for cropping so I could take a shot and save it with two keystrokes while still having the option to see what I have before saving and (if necessary) cropping it.