Assegnate 5 su 5 stelle

This add-ons does not work, it cannot find the installer or something.
Hopefully, you can fix it, thank you.

Edit: Clicking it several times finally got me to a prompt to add it to my search bar, but many times it would give me an error.

The addon is fully reviewed and OpenSearch compliant (there's actually no "installer", it's an xml file handled directly by the browser).

Unfortunately, sometimes the AMO site can be a little buggy (I believe I have traced it to a .js file here that users sometimes have problems with) and cause transient issues such as you have described. I am glad that you did manage to get things to work, though.