Hey! It in fact does work on this site.
Please look at the notice on the extension page.
You have to go to the add-ons manager about:addons in the URL bar, and manage volume control. Give it permission to "Access your data for all websites".

This site plays audio from an external page, so in order to access the iframe element the mutation observer in arrive.min.js needs api permission to view all site data.

Sorry for the delayed response, hope this works for you.