Actually I ve got a .cer certificate that has to be installed on all my domain computers. I ve created a GPO for that on my 2008 DC under: Computer configuration--policies--windows settings--security settings--public key policies and imported it on Trusted root certification authorities. it worked with Internet Explorer and Google Chrome. For mozilla i just followed this post https://4sysops.com/archives/group-policy-for-firefox-and-chrome/#comment-313021 Unfortunatelly it did't work. Am I missing something? I would appreciate your time and help on this.