If you happen to visit sites with self signed security certificates you will notice a error in firefox saying
This site uses an invalid security certificate.
The certificate is not trusted because it is self signed.
(Error code: sec_error_untrusted_issuer)
Firefox
shows this message many times while you browse that site. Fortunately
there is a way to add the certificate of that site manually. Here is how
to do it.
--- Go to Tools --> Options in the menu bar of firefox.
--- Now click on the Advanced tab and then on Encryption tab
--- Now click on the Certificates button shown in above image. You will see the certificate manager as shown below.
--- Now click on the Add Exception. You will see the following screen.
Here
add the site you want to get the certificate to. Then click on get
certificate. Firefox will check for the certificate and show it.
--- Now select Permanently store this exception and then press Confirm Security Exception.
That's it you will no longer get the self signed security certificate error for that site. You can also add other such sites following the above steps.
--- Go to Tools --> Options in the menu bar of firefox.
--- Now click on the Advanced tab and then on Encryption tab
--- Now click on the Certificates button shown in above image. You will see the certificate manager as shown below.
--- Now click on the Add Exception. You will see the following screen.
Here
add the site you want to get the certificate to. Then click on get
certificate. Firefox will check for the certificate and show it. 
--- Now select Permanently store this exception and then press Confirm Security Exception.That's it you will no longer get the self signed security certificate error for that site. You can also add other such sites following the above steps.
