You may indeed be visiting incorrect sites, but it is probably more likely that some software, such as some security scanner or filter is intercepting this and changing the certificate. You may need to change the software settings to work correctly with Firefox. Please make a note of the exact error messages and also list what security related software you use. These articles may help * [[How to troubleshoot the error code "SEC_ERROR_UNKNOWN_ISSUER" on secure websites]] * [["This Connection is Untrusted" error message appears - What to do]] * [[How do I tell if my connection to a website is secure?]]