In Chrome 73, a new security feature called Cross-Origin Read Blocking (https://www.chromestatus.com/feature/5629709824032768) prevents Wikiwands popup definitions from working. When you attempt to do a popup, the spinner stays forever, and in the Chrome Console log, you can see the following error message:

"Cross-Origin Read Blocking (CORB) blocked cross-origin response "https://en.wikipedia.org/w/api.php?..." with MIME type application/json. See https://www.chromestatus.com/feature/5629709824032768 for more details."

Relatedly: when the pop-up fails, the spinner stays forever. The popup should detect failure and remove the spinner when this happens, and ideally show a pop-up error with what happened.