What types of screenshots can I capture? There are several options for capturing screenshots:

• Capture parts of a page: When you move the mouse cursor over the page, different parts of the page will be automatically highlighted. Click on the one you want to save.
• Select a region of the page: Drag or click on the page to select a custom region of the page that you wish to capture. You can change the size and area to be captured using the marker points on the edge of the area.
• Capture a full page: Select Save full page from the menu in the upper right.
• Capture the visible part of a page: Select Save visible to save the area of the web page currently visible.

More information in: Take screenshots in Firefox

I have always used; Windows > Start > search box > Snip. Select Snipping Tool. Use a compressed image type like PNG or JPG to save the screenshot. Save the picture(s) to your desktop, or wherever. Press the Reply button. Then press the Add images; Browse button.