When I test add-on on Windows 10 and Firefox 94.0.2, on the debugging console window, I encounter two warnings:
The Web Console logging API (console.log, console.info, console.warn, console.error) has been disabled by a script on this page
Layout was forced before the page was fully loaded. If stylesheets are not yet loaded this may cause a flash of unstyled content.
I have no ideas of what caused the two warnings, thank you for your help!