To support the answer by @oberstet, if the cert is not trusted by the browser (for example you get a "this site is not secure, do you want to continue?") one solution is to open the browser options, navigate to the certificates settings and add the host and post that the websocket server is being served from to the certificate provider as an exception.
for example add 'example-wss-domain.org:6001' as an exception to 'Certificate Provider Ltd'.
In firefox, this can be done from 'about:preferences' and searching for 'Certificates'