The TAG only mentions Safari on iOS, but Safari on Mac is equally fussy about not allowing Websocket communication to bad certificates.
To make things worse, the method to work around it is different. Clicking on the certificate just gives you the PEM text in the browser. What you have to do is expand the first dialog that complains a bad certificate and tell Safari to always accept this certificate. If you've already dismissed that dialog then you have to restart Safari and try again.