There was a Windows 7 update and a Firefox 27 update today. Unfortunately I didn't think to do one at a time. First I noticed gmail wasn't displaying graphics properly in the chat window. Then the Firefox check-add ons link didn't do anything, just displayed "Loading Data" and never loaded anything. I went to the Add-ons for my Firefox and it displays the error "This Connection is Untrusted. You have asked Firefox to connect securely to services.addons.mozilla.org, but we can't confirm that your connection is secure." and "services.addons.mozilla.org uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. (Error code: sec_error_unknown_issuer)" There is no way to add a certificate exception, so I cannot use the add-ons page. Other websites using https either do not display correctly or also display the "This Connection is Untrusted" error. I have done pretty much everything suggested on forums and FAQ: I've reset Firefox, I've deleted the cert8.db file and other extension files in my profile. I've started in safe mode, tried a different profile. Did a clean install to Firefox 26, and I still get this error message. I saw suggestions that had to do with a Security installation, which I don't have, might there be an equivalent for McAfee? I am using a corporate computer and don't have control over anti-virus or proxy settings. I had to install Chrome just to post this question as "Ask This" button did not respond at all on IE.