I’m updating my old Ad Limiter add-on. Here’s its preferences menu. It works fine in Release Firefox 78.0.1 64 bit (Linux). But in Developer Firefox 78.0b9 on the same machine, with the add-on loaded from a local file, the drop-down menu won’t drop. No errors in the browser console. Clicking on the drop-down arrows just doesn’t do anything. The other add-on functions work the same on both platforms.