Could you click the Advanced button on that error page, then copy/paste the more technical explanation into a reply?

Generally speaking, when you get certificate errors for most secure sites, the problem usually is one of the following:

(1) Error in your system's date, time, or time zone, which throws off certificate validity checks. Sometimes allowing computers to use an internet-based time source can introduce this problem.

(2) Firefox not being set up to work with your security software that intercepts and filters secure connections. Products with this feature include Avast, BitDefender, Bullguard, ESET, and Kaspersky; AVG LinkScanner / SurfShield can cause this error on search sites.

(3) On Windows 10, Firefox not being set up to work with the parental control software Microsoft Family Safety. (To test by turning it off, see: http://windows.microsoft.com/en-us/wi.../turn-off-microsoft-family-settings)

(4) Malware on your system intercepting secure connections.

If you have any of those specific security products:

That would be the first thing to check. This support article will walk you through it: How to troubleshoot security error codes on secure websites.

If none of those ring a bell:

You could inspect a sample certificate to see whether that points to the culprit. If you want to try that now, here's how I suggest starting:

Load my test page at: https://jeffersonscher.com/res/jstest.php

You likely will get an error page. Expand the "Advanced" button and look for an Add Exception button.

Note: You don't need to complete the process of adding an exception -- I suggest not adding one until we know this isn't a malware issue -- but you can use the dialog to view the information that makes Firefox suspicious.

Click Add Exception, and the certificate exception dialog should open.

Click the View button. If View is not enabled, try the Get Certificate button first.

This should pop up the Certificate Viewer. Look at the "Issued by" section, and on the Details tab, the Certificate Hierarchy. What do you see there? I have attached a screen shot for comparison.

1- mail.yahoo.com uses 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 https://mail.yahoo.com/

Peer's Certificate issuer is not recognized.

HTTP Strict Transport Security: true HTTP Public Key Pinning: false

Certificate chain:

MIIGmzCCBYOgAwIBAgIJAKkCgo2wJU6dMA0GCSqGSIb3DQEBCwUAMGAxLTArBgNV BAMMJEJpdGRlZmVuZGVyIFBlcnNvbmFsIENBLk5ldC1EZWZlbmRlcjEMMAoGA1UE CwwDSURTMRQwEgYDVQQKDAtCaXRkZWZlbmRlcjELMAkGA1UEBhMCVVMwHhcNMTYw NjE1MDAwMDAwWhcNMTgwNjA5MjM1OTU5WjCBhjELMAkGA1UEBhMCVVMxEzARBgNV BAgMCkNhbGlmb3JuaWExEjAQBgNVBAcMCVN1bm55dmFsZTETMBEGA1UECgwKWWFo b28gSW5jLjEfMB0GA1UECwwWSW5mb3JtYXRpb24gVGVjaG5vbG9neTEYMBYGA1UE AwwPbG9naW4ueWFob28uY29tMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKC AQEAx6vx0xAHQ6bIV5HmeZrpimI/jzq8qQ1bZOVhTeTfVOQ3p1djwOPNZn6YgBwc IRmXgczh6BhF4YIVnmTncR+UzSBiCsk31/bbnIITKBwZ4G1jl4BiXLdWxY6mU80o pG9Dc8eLMQjvcyoFaSfRAPOfRtkTGfBpqqdKMfNGi8g8qKjbmvoI+UZPlfePz+sF ilSBw8qAAQpGHv6fNsI6VspMBepbYYyWAU+rN2nELDOeU8A/vR/oAl6G+V9ZjP3v uuwvtv98qRi4nzlztixRuXxLHe9aNVdkol0V5u5dVKM2oLUis8ea4T9iY14O3/kj cJmPxoWxccl2AiDDqXCzh3AdUwIDAQABo4IDLzCCAyswggMnBgNVHREEggMeMIID GoIPbG9naW4ueWFob28uY29tghEqLmxvZ2luLnlhaG9vLmNvbYIQKi5lZGl0Lnlh aG9vLmNvbYIQKi5tYWlsLnlhaG9vLmNvbYIObWFpbC55YWhvby5jb22CEm1haWwu eWFob28taW5jLmNvbYITZmIubWVtYmVyLnlhaG9vLmNvbYIRYXBpLnJlZy55YWhv by5jb22CDmVkaXQueWFob28uY29tghN3YXRjaGxpc3QueWFob28uY29tghRlZGl0 LmluZGlhLnlhaG9vLmNvbYIUZWRpdC5rb3JlYS55YWhvby5jb22CFWVkaXQuZXVy b3BlLnlhaG9vLmNvbYIYZWRpdC5zaW5nYXBvcmUueWFob28uY29tghJlZGl0LnRw ZS55YWhvby5jb22CF2xlZ2FscmVkaXJlY3QueWFob28uY29tggxtZS55YWhvby5j b22CGG9wZW4ubG9naW4ueWFob29hcGlzLmNvbYITc3Vic2NyaWJlLnlhaG9vLmNv bYIVZWRpdC5zZWN1cmUueWFob28uY29tghVlZGl0LmNsaWVudC55YWhvby5jb22C GGJ0LmVkaXQuY2xpZW50LnlhaG9vLmNvbYIddmVyaXpvbi5lZGl0LmNsaWVudC55 YWhvby5jb22CGG5hLmVkaXQuY2xpZW50LnlhaG9vLmNvbYIUYXUuYXBpLnJlZy55 YWhvby5jb22CEGF1LnJlZy55YWhvby5jb22CEG9wZW5pZC55YWhvby5jb22CHHJv Z2Vycy5lZGl0LmNsaWVudC55YWhvby5jb22CI25vdGlmeS5yb2dlcnMuZWRpdC5j bGllbnQueWFob28uY29tgiBub3RpZnkuc2JjLmVkaXQuY2xpZW50LnlhaG9vLmNv bYIkbm90aWZ5LnZlcml6b24uZWRpdC5jbGllbnQueWFob28uY29tgh1sZGFwLmJ0 LmVkaXQuY2xpZW50LnlhaG9vLmNvbYIPYzUuYWgueWFob28uY29tghBjNWEuYWgu eWFob28uY29tghBtbG9naW4ueWFob28uY29tMA0GCSqGSIb3DQEBCwUAA4IBAQBB FTYU+6OdEXFai+i+WQ7g/i8xWeGtJkVfDZ7iOLRF89tLEMunPDhmQjKZqT5n7l32 Ci/XbsLuNsDNRR9n4XHHPUQiNNjmZCZH811ndpxkiQbUZTy6b4bBFkiEPkVaRlp3 XmSRM3f7tc8j7b+kUTCcj8qL8uLVL28EaKZkTktJtwMMmY8NncarRv8hW/5tw7tD YMPyFuyNssUbPRWOcjiJw6LkS0YfHKOSI/yz/ahZQT6VzzYuOtCus7e1fspPo9Ef DkFJpP+nGnOy+Q1gSffCFpszg69fx9cAAayEXLkrMXHrDUAj9wt5YiNsB4bK85q2 PLJzGGj5OTNNwQO9tXBD

2- www.google.com uses 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

3- facebook.com uses 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 https://facebook.com/

Peer's Certificate issuer is not recognized.

HTTP Strict Transport Security: true HTTP Public Key Pinning: true

Certificate chain:

MIIEEjCCAvqgAwIBAgIJAIuVowHS24cRMA0GCSqGSIb3DQEBCwUAMGAxLTArBgNV BAMMJEJpdGRlZmVuZGVyIFBlcnNvbmFsIENBLk5ldC1EZWZlbmRlcjEMMAoGA1UE CwwDSURTMRQwEgYDVQQKDAtCaXRkZWZlbmRlcjELMAkGA1UEBhMCVVMwHhcNMTQw ODI4MDAwMDAwWhcNMTYxMjMwMTIwMDAwWjBhMQswCQYDVQQGEwJVUzELMAkGA1UE CBMCQ0ExEzARBgNVBAcTCk1lbmxvIFBhcmsxFzAVBgNVBAoTDkZhY2Vib29rLCBJ bmMuMRcwFQYDVQQDDA4qLmZhY2Vib29rLmNvbTCCASIwDQYJKoZIhvcNAQEBBQAD ggEPADCCAQoCggEBAMer8dMQB0OmyFeR5nma6YpiP486vKkNW2TlYU3k31TkN6dX Y8DjzWZ+mIAcHCEZl4HM4egYReGCFZ5k53EflM0gYgrJN9f225yCEygcGeBtY5eA Yly3VsWOplPNKKRvQ3PHizEI73MqBWkn0QDzn0bZExnwaaqnSjHzRovIPKio25r6 CPlGT5X3j8/rBYpUgcPKgAEKRh7+nzbCOlbKTAXqW2GMlgFPqzdpxCwznlPAP70f 6AJehvlfWYz977rsL7b/fKkYuJ85c7YsUbl8Sx3vWjVXZKJdFebuXVSjNqC1IrPH muE/YmNeDt/5I3CZj8aFsXHJdgIgw6lws4dwHVMCAwEAAaOBzTCByjCBxwYDVR0R BIG/MIG8gg4qLmZhY2Vib29rLmNvbYIOKi5mYWNlYm9vay5uZXSCCCouZmIuY29t ggsqLmZiY2RuLm5ldIILKi5mYnNieC5jb22CECoubS5mYWNlYm9vay5jb22CDyou bWVzc2VuZ2VyLmNvbYIOKi54eC5mYmNkbi5uZXSCDioueHkuZmJjZG4ubmV0gg4q Lnh6LmZiY2RuLm5ldIIMZmFjZWJvb2suY29tggZmYi5jb22CDW1lc3Nlbmdlci5j b20wDQYJKoZIhvcNAQELBQADggEBACAaWTNt9O0sq42EG/oJmAKAvDF75Bp9D9Hx whejboXCLdEdSukI5/9nSBAeAhbVWugZnVDPUk/SD8NHKrf+ndqnEb3qhMQGQUWp 6i/N8I/ScXrYjKElaUcW24jic00/cHPPbOViuMOwFy1zVhQYApoLuXOgvdhp74Dk HrJrjNNP9+dqQJbaCnI6GJhez93w5OLvPMNKpgtHIDWwperQ5YpRd3EMVkHAkVzj W1w21kf1eHViPTRfe+imcFvGk/7wkdarA+/iDskOWQgLvOpk7/VAMPhfm6Dz15YO clyngO1XS2OWDOw7MQKhyFr9n4zD28UdX6XxqtLB/WhyzQwHTaw=

4- technet.microsoft.com uses 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 Although HERE I was offered to set an EXCEPTION which was accepted, but I could only see the simple (no html) pages.

IE functions normally. System scan with BitDefender IS 2015 Scan with Malwarebytes 2015 Cleared cache & cookies & history

BitDefender! See: How to troubleshoot security error codes on secure websites

My Win 7 was already set the way I want it, but the new Win 10 Bitdefender still had the Screen SSL active. I still insist, that FF is typical in that it makes it very difficult for users know where to look for help, first getting through the jungle of FAQs, but I'm typically far from perfect too Thanks!!!!

There are people who try to improve this site behind the scenes. If you find a site that does it well, please point out that one as an example. I think all software companies struggle.