hi obould, tls 1.0 is still supported in firefox - see the "protocols" section of https://www.ssllabs.com/ssltest/viewMyClient.html

if you receive error messages it's probably because particularly insecure/broken cipher suites are used on a web server. in order to know what's going on and if there are workarounds it will probably be necessary to know the url of the websites in question or at least the error code that is shown on these sites...

Hello,

this is the error I get:

An error occurred during a connection to .... SSL received a weak ephemeral Diffie-Hellman key in Server Key Exchange handshake message. (Error code: ssl_error_weak_server_ephemeral_dh_key)

   The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
   Please contact the website owners to inform them of this problem.

if you receive that error code when accessing a site, this means that the webserver you're trying to reach is vulnerable to the recently published logjam attack and therefore firefox won't connect: http://arstechnica.com/security/2015/05/https-crippling-attack-threatens-tens-of-thousands-of-web-and-mail-servers/ https://weakdh.org/

unfortunately this can only be fixed by changing the configuration on the affected web-server.