Can confirm, does absolutely nothing on Win10 with newest Firefox. Window opens, but all bars are empty/cant be changed and the buttons change color when clicked but that's it.

"Uncaught (in promise) Error: Script 'moz-extension://72149dd7-64d2-4a9d-b1af-4f8eea9e6f73/audio_processor.js' result is non-structured-clonable data audio_processor.js
apply self-hosted:2610
applySafeWithoutClone resource://gre/modules/ExtensionCommon.sys.mjs:689
applySafeWithoutClone resource://gre/modules/ExtensionCommon.sys.mjs:688
wrapPromise resource://gre/modules/ExtensionCommon.sys.mjs:960"