iNaturalist API Recommended Practices suggest specifying a user agent header, but it is disallowed by CORS

[frewsxcv]

From https://www.inaturalist.org/pages/api+recommended+practices:

If writing software to interact with the API, please consider using a custom User Agent to identify your application, or iNaturalist username, or something we might use to differentiate your requests
The User Agent can be set with an HTTP header, e.g. User-Agent: [[application or user name]

But if you specify this, then clients that honor the Access-Control-Allow-Headers (e.g. Firefox) will not be able to complete the request since User-Agent is not allowed.