Just updated Firefox to v66, and after that lots of web pages failed to load with error NS_ERROR_NET_INADEQUATE_SECURITY (including KaOS, Google and DuckDuckGo). It seems that FF started to enforce some kind of TLS profile, making lots of pages to break.
To remove the enforcing policy, go to about:config and look for network.http.spdy.enforce-tls-profile and set it to false. Security is good, but not if it breaks half the internet 🙂