A Firefox-Only Minimap

From the discussion:

> The function allows you to display images of arbitrary HTML elements on your page! And the best thing is: it's live! Try selecting some text or scroll around to see lazy-loaded images kicking in. It's magic!

Edit: I'm not sure if Firefox is the only browser to support it anymore and I see LibreWolf that is forked from the newest Firefox doesn't show it so I guess there is some browser sniffing (uncool) going on here too, not only feature detection.