Check out who has issued this certificate.

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• Click the link at the bottom of the error page: "I Understand the Risks"

Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".

• Click the "View..." button and inspect the certificate and check who is the issuer of the certificate.

You can see more Details like intermediate certificates that are used in the Details pane.

If "I Understand the Risks" is missing then this page may be opened in an (i)frame and in that case try the right-click context menu and use "This Frame: Open Frame in New Tab".

Check the connection settings.

• Tools > Options > Advanced > Network : Connection > Settings
• https://support.mozilla.org/kb/Options+window+-+Advanced+panel

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

• https://support.mozilla.org/kb/Firefox+cannot+load+websites+but+other+programs+can

Hi I am repeating theis reply as when I clicked on post reply it seems to have disappeared. Thanks for your reply, I do not pretend to understand the result of a request to view the certificate, I have attached it and don't think I would trust it. Thanks again, Boyd (mactoshb)

You seem to be using the Fiddler web proxy and that proxy sends its own certificate.

• http://www.fiddler2.com/fiddler2/

You will either have to disable Fiddler or accept this trusted message.
I don't know if you can install a root certificate from Fiddler.

Hi, thanks for your further reply, I see what you say but do not have a clue how to disable fiddler or get a root certificate. Can you advise me on how to go about it? I have no add ons other than two to do with Norton and no extentions and Start/ search/fiddler only comes up with your reply to my question, no mention in Remove progs. I have to go out now so any further reply to you will be delayed but I very much appreciate your efforts Boyd

please check in firefox > options > advanced > network > connection - settings... if firefox is set up to directly connect to the internet ('no proxy').

When I returned home and switched on the computer "Spyhunter" which I have installed stuick up a message saying my settings appeared to have been changed to a proxy server and asked if I wanted Spyhunter to correct the changes, I gave permission and the problem sems to have been solved. I think that confirms your diagnosis that the problem was I was using a proxy server, so thanks for your help and I will save all the answers in case it happens again Boyd