After Clean Install Of Windows 10 Pro X64,Firefox Dont Want To Connect To Sites : with https xxxfaceyyyyy This Is from Firefox This Connection is Untrusted You have asked Firefox to connect securely to xxxfaceyyyyy but we can't confirm that your connection is secure. Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do? If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue. This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox only connect to it securely. As a result, it is not possible to add an exception for this certificate. faceuses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported. (Error code: sec_error_unknown_issuer)
I had similar problems with firefox since version 38 onwards - some sites do not open (http or https) although they open in chrome and other browsers on the same machine instantly at the same time. But when I disconnect my router and reconnect the sites again start opening in Firefox also without giving any error.
If the user account you're using has family safety enabled you have to import family safety's certificates to Firefox's certificate repository. Another possibility is your antivirus software scanning HTTPS traffic and causing this because it didn't add its certificates to firefox.