Sorry, I probably should have been more explicit. I was also referring to the part where they suggested disabling weak ciphers, like explicitly stated in GP, RSA. That's what caused problems for me.

That depends on what do you consider as a weak cipher, I do have security.ssl3.rsa_des_ede3_sha set to false in Firefox as well. If you mean all ciphers that don't have forward secrecy then I guess it may broke a lot more.

edit: i also have security.ssl3.rsa_aes_256_sha disabled, so my only non forward secrecy cipher fallback is TLS_RSA_WITH_AES_128_CBC_SHA

I would suggest to avoid disabling ciphers in your browser as it can damage your privacy.

Is there an effort to build a whitelist for sites using old TLS versions?

I don't have any plans for creating such whitelist, if webmasters and sysadmins don't respond to my emails they will be forced by browsers anyway - in one year the most commonly used browsers will disable TLS 1.0 and 1.1 with an update [0]. For now it serves as a good warning that such webserver isn't updated and might be hacked sooner or later. With pretty much every distribution released in last ten years you can patch it so that apache/nginx or whatever will use TLS 1.2 and if you're using something even older it probably shouldn't be on the internet anyway.

[0] https://www.zdnet.com/article/chrome-edge-ie-firefox-and-saf...