TLS 1.2 and 1.3 are the supported TLS protocols. TLS 1.0. and TLS 1.1 have been deprecated in current Firefox releases and have been disabled. You can still enable TLS 1.0 via the button on the error page although this is not recommended. Once you have enabled these older TLS protocols you will have to go to about:config to disable TLS 1.0 and 1.1 once again. *about:config => security.tls.version.enable-deprecated = false *https://support.mozilla.org/en-US/kb/about-config-editor-firefox