I looked into this popup that you mentioned, and I updated the extension to now also remove the element responsible for this. Update to the new version 0.4.0 and this should then be gone. :)
Edit: That sucks! The extension didn't change and I tested it right now on two different devices running Firefox v130 and on both the extension still works as expected. Might be something weird with your Firefox installation (or Reddit is up to something)? What a bummer!
