Summarize the following:
You'll find it in the Start menu on Windows and in the Applications folder on macOS. Firefox comes with a built-in screenshot tool that can quickly capture the current webpage. Firefox Screenshots will capture the webpage only, not the browser buttons and menus. If you want to take a screenshot of other parts of the screen, check out How to Take a Screenshot in Microsoft Windows or How to Take a Screenshot on a Mac. You'll have the option to capture any part of the page. The address bar is where the URL appears (at the top of the browser) and the three dots are on the far-right edge. A menu will expand. If it's your first time taking a screenshot with Firefox, you'll see a welcome screen with an arrow icon on the right side. Click the arrow to advance to the next screen in the tutorial, and continue clicking until you reach the end. To skip the tutorial, click SKIP below the window. Once you choose a screenshot type, a preview will appear. You have four options from which to choose:  Click Save Visible at the top-right corner to take a screenshot of the part of the webpage that appears on the screen now. Click Save full page at the top-right corner to take a screenshot of the entire page, including the parts that don't appear on the screen right now. To take a screenshot of just one part of the page, click and drag the mouse to surround the part you want to capture. Another option to capture part of the page is to hover the mouse cursor over the desired region until a dotted line appears around it, and then click that region. This saves the screenshot file to your Downloads folder. If you want to paste the screenshot into a file or window rather than saving it as a separate image file, click the Copy button instead, right-click the desired location, and then click Paste.

Summary:
Open Firefox on your computer. Go to the page you want to screenshot. Click the three dots in the address bar. Click Take a Screenshot. Select a screenshot option. Click Download to save your screenshot.