You may have expired or otherwise corrupted Microsoft intermediate certificates.<br /> You can check that in the Certificate Manager on the Authorities tab under GTE Corporation and Microsoft Internet Authority. *Tools > Options > Advanced : Encryption: Certificates - View Certificates ---- Try to rename the cert8.db file in the Firefox profile folder to cert8.db.old or delete the cert8.db file to remove intermediate certificates that Firefox has stored. If that helped to solve the problem then you can remove the renamed cert8.db.old file.<br /> Otherwise you can rename (or copy) the cert8.db.old file to cert8.db to restore the previous intermediate certificates.<br /> Firefox will automatically store intermediate certificates when you visit websites that send such a certificate. If that didn't help then remove or rename secmod.db (secmod.db.old) as well. Also check the date and time in the clock on your computer: (double) click the clock icon on the Windows Taskbar. *https://support.mozilla.org/kb/Secure+Connection+Failed