I think that this can happen if there is a mismatch between the TLS protocol the server supports and the TLS protocol your browser supports. Using a proxy can also cause this, but is also possible that the server doesn't support modern TLS versions (TLS 2 and 3). Make sure that these prefs are default on the <b>about:config</b> page. *security.tls.version.max (4) *security.tls.version.min (3) *https://support.mozilla.org/en-US/kb/about-config-editor-firefox