Why won't certain websites open?

Question

Just in the last few days some major websites have not been opening - Google, BT Yahoo, and Facebook, yet some lesser known ones which I use are working well. The following message appears after a prolonged period (10-20 seconds) :
"Secure Connection Failed
An error occurred during a connection to www.google.com. Cannot communicate securely with peer: no common encryption algorithm(s).
Error code: ssl_error_no_cypher_overlap"
Due to the fact that Google is one of the problematic sites I can't even Google it, although when I ask a friend to do so, the results seem to point to a problem within Firefox. I am unsure if this is correct, as IE is also problematic with these sites too. I have scanned my PC for viruses and it appears to be clean. My ISP has checked and they can see no problems with the network. I can also ping external sites, as well as the router itself. I don't seem to recall these issues until the latest update was installed, although that might be coincidence.
Any help will be gratefully received.

Answer 1

By default, Firefox will try the most secure protocol (TLS 1.2) and progressively drop down to older and more vulnerable ones (all the way back to SSL 3.0). If these settings have been changed, some sites might not connect.
Can you check the SSL levels Firefox is set to use? Here's how:
(1) In a new tab, type or paste '''about:config''' in the address bar and press Enter. Click the button promising to be careful.
(2) In the search box above the list, type or paste '''tls''' and pause while the list is filtered
(3) If the following preferences are bolded and indicate "user set", make a note of what they are. Then use right-click > Reset to restore their default values and try the sites again.
security.tls.version.'''min''' ''(usually 0)''
security.tls.version.'''max''' ''(usually 3)''
Any difference?