Nothing to configure it: no "Options" page for the extension, no new button... I only got a "Screenshot" and a "Loop" button on youtube webpages, that's all.
Answer: I have 11 extensions installed, and have tested hundreds others. I also use Firefox since its creation.
sounds like you have not used any browser extensions before. please be informed that extensions usually have an options page and a browser icon. (And in our's, the first toggle even enables an icon on youtube.com too - if you will.)
