Accessing a local application with XHR request worked in chrome, but Firefox gave the error that Cross-Origin Request Blocked and in fact didn't even read the stream.
This is not a cors problem per se, but the fact that Firefox gave an exception on the certificate which is self-signed.
What must be done:
In firefox dev tools, open the network tab and copy the url accessed with Options (the devtool gave no status for it)
copy the adress in the browser (Firefox) : https://localhost:1234/yoururl