I have
Bitdefender Internet Security 2015
Build 18.12.0.958
Firefox 31
Windows 7 x64 Service Pack 1
I get this on some https sites
This Connection is Untrusted
You have asked Firefox to connect securely to www.facebook.com, but we can't confirm that your connection is secure.
Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified.