Sometimes there is a menu bar and other things above or surrounding an image. Apparently, the Mozilla "take a screenshot" gets confused, and although other parts of the page are above, they end up IN the image when using the screenshot. Here is an example. The selection box was ONLY of the photo (which scrolled on and off the screen horizontally and vertically). The box only surrounded the image, yet here is what it captures.. Mozilla 57.0 64bit on W10.