Creator of the Zoom Escaper here... Sadly it relies on a web audio feature that's chrome only. Also too bad because I use firefox as my primary browser.
1: https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_A...
Its MDN doc (https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaEl...) shows it as a not-quite-finalized feature, but even so, seems odd to have a pref just for it.
Granted, a glitchy audio implementation might be just the thing for this use case...
Mentioing the info from kelnos' comment would be excellent.
If someone wants to use this they should have no problem running in chrome.