Firefox cannot access the Zotero API using CORS. It seems like the problem is the Host header. If I make a request to https://api.zotero.org/itemTypes in Chrome, the Host will be api.zotero.org. If I do the same in Firefox, it will be test.workingnotes.org (or whatever the domain is of the current script). Zotero doesn't respond to that. Not sure what to do, except to proxy requests.