For further information about this issue, please refer to these Mozilla support articles:

• What do the security warning codes mean?
• Secure connection failed and Firefox did not connect

Note: Please ensure that your system date and time settings are configured correctly.

Thank you for the reply.

I've cleared my cache and cookies, my system time and date are correct and still the same issue.

Any other suggestions would be appreciated.

When you get connection errors for nearly all secure sites, the problem usually is one of the following:

(1) [Already ruled out] 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 / nod32, and Kaspersky; AVG LinkScanner / SurfShield can cause this error on search sites.

If you have any of these products: This support article will walk you through checking for this problem: How to troubleshoot security error codes on secure websites.

(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 #1-#3 don't seem relevant, you could inspect a sample certificate to see whether that points to the culprit. Here's how:

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

If you do not get a connection error, stop. The rest of this isn't applicable.

Expand the "Advanced" button on the error page 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.

Edit: had to update the image due to a new certificate being issued recently.