Please update to the most recent version of Firefox:

• Update Firefox to the latest release

This tls fallback issue was solved in version 37.0.1

The website uses TLS 1.2 for me, so they may have fixed their server(s).

Note that the Browser Console (Firefox/Tools > Web Developer) shows:

This site makes use of a SHA-1 Certificate; it's recommended you use certificates with signature algorithms that use hash functions stronger than SHA-1.

• TLS_RSA_WITH_AES_128_CBC_SHA

Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"