This extension allows you to find and use most of the old, working extensions (that used XUL/XPCOM) that have been removed from the Firefox add-on site by the utter fucking idiot assclown numpty dipshits at Mozilla.

Install it, click the button, find software that actually works. Note that you must be using an older version of Firefox, Waterfox, Pale Moon, etc. (Back when browsers actually did what the user wanted rather than what corporations want.)