1. In Firefox, press Shift+F2.
This opens up the Firefox console at the bottom of the screen which enables you to issue commands right from the webpage.
2. Enter the following command and press Enter:
screenshot --fullpage3. A screenshot image file of the whole web page will be made in your Downloads folder.
To close the console, simply press Shift+F2 again. You can use this command with different parameters to achieve different results:
--fullpage
Takes a screenshot of the entire web page even the parts not scrolled to.--delay <number>
Takes a screenshot after the specified delay (in seconds).--clipboard
Takes a screenshot and copies it to the clipboard.--chrome
Takes a screenshot of the whole Firefox window, not just the webpage.