Firefox has a powerhouse suite of Developer tools that comes standard. Among them is the ability to take a screenshot of the whole page!
First, enable the feature. Press ‘Ctr+Shift I‘ to display the Developer Tools. Click on the Gears icon, scroll down to tick ‘Take a screenshot of the entire page’
Then, whilst on any page, press ‘Shift+F2‘ to call up the command line interface, and type ‘screenshot –fullpage‘ then Enter.
A fullpage screenshot of the page will now appear in your Download directory!