I am a freelance contractor who operates social media accounts, content creation, and online marketing- so this is a huge ordeal. As of today, when I go to Facebook.com, Hotmail, Twitter, and even the Squarespace pages I operate, I get redirected to a page displaying this message _______________________________________ "twitter.com has a security policy called HTTP Strict Transport Security (HSTS), which means that Firefox can only connect to it securely. You can’t add an exception to visit this site. The issue is most likely with the website, and there is nothing you can do to resolve it. If you are on a corporate network or using anti-virus software, you can reach out to the support teams for assistance. You can also notify the website’s administrator about the problem." If I select 'more information', I receive this- _____________________________________________ Someone could be trying to impersonate the site and you should not continue. Websites prove their identity via certificates. Firefox does not trust twitter.com because its certificate issuer is unknown, the certificate is self-signed, or the server is not sending the correct intermediate certificates. Error code: SEC_ERROR_UNKNOWN_ISSUER View Certificate This is obviously catastrophic in terms of impact for my job. Granted, I can (and have) downloaded a different browser. I would like to continue using Firefox, what on earth are my options here?