Check the date and time and time zone in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

Check out why the site is untrusted and click "Technical Details to expand this section.
If the certificate is not trusted because no issuer chain was provided (sec_error_unknown_issuer) then see if you can install this intermediate certificate from another source.

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• Click the link at the bottom of the error page: "I Understand the Risks"

Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".

• Click the "View..." button and inspect the certificate and check who is the issuer of the certificate.

You can see more Details like intermediate certificates that are used in the Details pane.

If "I Understand the Risks" is missing then this page may be opened in an (i)frame and in that case try the right-click context menu and use "This Frame: Open Frame in New Tab".

• Note that some firewalls monitor (secure) connections and that programs like Sendori or FiddlerRoot can intercept connections and send their own certificate instead of the website's certificate.
• Note that it is not recommended to add a permanent exception in cases like this, so only use it to inspect the certificate.

Clicking "Get Certificate" in the Add Exception menu just refreshes the same thing. "Certificate is not trusted, because it has not been verified by a recognized authority using a secure signature.

What does it say under the "Technical Details" ?

Can you also attach an image of the Certificate Manager window and possibly of the Details pane with the issuer of the certificate selected that opens if you click the View button?

Here are the images.

The second screenshot shows that the certificate is issued by your Microsoft Family Safety security software.

You would have to check that software to see if you can install the root certificate. You can also check this in another browser like IE and export the Microsoft Family Safety certificate and import the certificate in the Firefox Certificate Manager. You will have to set the appropriate trust bits when prompted.

I'm not sure how to do this. Do I export the certificate out of Internet Explorer? If so, how do I do that? And how do I import certificates in Firefox?

Thank you so much for you help!

In Firefox you can import the certificate in the Certificate Manager.

• Tools > Options > Advanced > Certificates: View Certificates
• https://support.mozilla.org/kb/Options+window+-+Advanced+panel

You should be able to click the padlock in the location/address bar in IE to inspect the certificate chain.

I checked the certificate path in IE, and it says that the certificate is issued by Microsoft Family Safety, yet the website still works. Why is this?

You need to export the Microsoft Family Safety certificate that shows in the second screenshot and import this certificate in Firefox.

By the way, after you resolve this issue, you'll find that many secure sites still are not considered to have a verified identity. This is because Firefox only treats Extended Validation (EVSSL) certificates as verifying identity. Those are the ones with the green lock.