Firefox fails on CORS resource, while Chrome and Safari work

Question

I have a seemingly correct resource backed by a CouchDB installation. Requests are made using JS Axios. Both Chrome and Safari work, Firefox 65.0 fails however with

Answer 1

@sideshowbarker thanks for the hint - indeed, the behaviour was due to an extension - namely this one https://addons.mozilla.org/en-US/firefox/addon/cross-domain-cors/ after disabling this extension cors worked as expected!