Some extensions that allow to save a page as an image:

• Abduction!: https://addons.mozilla.org/firefox/addon/3408
• FireShot: https://addons.mozilla.org/firefox/addon/5648
• Pixlr Grabber: https://addons.mozilla.org/firefox/addon/9924/
• WIPS: https://addons.mozilla.org/firefox/addon/146364/
• Screengrab: https://addons.mozilla.org/firefox/addon/1146

easily on windows OS just click (print screen button) or (Shift + print screen button )*

• to capture the opened window picture

Print screen only allows to save the current window. The extensions can save the entire page, including parts that are hidden and require scrolling down to get in view.

If you're using Windows, click the Windows icon (in the bottom left hand corner of your screen), then 'all programs' then 'accessories', then 'snipping tool'

In the little box that opens, there's a menu under 'new' which allows you to take the whole page, a rectangle, or a freehand selection. You can highlight things in different colours with the 'pen' tool before saving.

You can add the screen shots as an attachment to emails, or 'insert picture' to have them in the main body of an email or document