The card doesn't appear in the UI editor list.
Trying to add it manually results in a configuration error: Custom element doesn't exist.

I can add the card from a chrome-based browser or the companion app but displaying the dashboard on Firefox causes the same configuration error.

I noticed this two lines on the dev console:

- Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://unpkg.com/lit@3.1.0/index.js?module. (Reason: CORS request did not succeed). Status code: (null).
- Module source URI is not allowed in this document : « https://unpkg.com/lit@3.1.0/index.js?module ».