I don't quite understand the 'screenshot' option because it offers two options (Save full page and Save visible) and in my opinion they do the same thing.
'Save visible' just saves what you can seen on your screen at that moment in time, whereas 'Save full page' will also save anything on the page that you can only see by scrolling the page - i.e. anything above or below the 'visible' portion of the page that you're currently viewing.
If I have an image in a tab and zoom in on that tab, the buttons are also affected by the zoom when using the screenshot option, making them difficult to see depending on the zoom level used.