Are you still getting this error? Have you enabled the following preference and, if so, thank you for testing, but maybe it isn't ready for prime time? (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk. (2) In the search box above the list, type or paste '''esni''' and pause while the list is filtered (3) If the '''network.security.esni.enabled''' preference is bolded and "modified" to true, you could double-click it to switch to the default value of false

See also: *https://blog.mozilla.org/security/2018/10/18/encrypted-sni-comes-to-firefox-nightly/