Before a deep dive, if all secure sites are untrusted, one potential reason is a problem with the date on your computer, such as being one year ahead or behind.

After ruling that out...

A common problem recently is Firefox not being set up to work with your security software. Some security suites include a filtering feature. In order to filter secure connections (HTTPS URLs), the security software presents a fake certificate to Firefox so it can intercept and stand in the middle of the secure connection. To have Firefox trust these certificates, you may need to do something such as import a root certificate, or click something in your security software's settings.

But it also could be spyware.

If you have use the Add Exception button, please check the "Issued by" section on one or two of the exceptions you've made to learn more about the source of this issue.

orange Firefox button (or Tools menu) > Options > Advanced > Certificates mini-tab > "View Certificates" button > Servers tab

Click a certificate and use the View button. The kind of issuer you might find is:

• Name associated with your security software, such as ESET, BitDefender, etc.
• Sendori (indicates unwanted software from Sendori)
• FiddlerRoot (indicates unwanted software named similarly to BrowserSafeguard, BrowserSafe, SafeGuard)
• Something else

If you have not added Exceptions, you can click the Add Exception button in the last section of error page, then in the dialog click View Certificate or Get Certificate to see the Issued by section. You do not need to finish adding an exception.

What issuer do you see?

Date is fine. And I have not done anything with my security software. Problem just started out of the blue. And when I try the "add exception" button, nothing happens. Thanks. R

When you click the Add Exception button, Firefox normally displays a dialog with more information.

You also can check the certificate for the same site in Internet Explorer. You can click the lock icon on the address bar to access the details and check the issuer/issued by section.

To rule out your extensions as a possible culprit, could you try the sites in Firefox's Safe Mode? That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled (Flash and other plugins still run)

In the dialog, click "Start in Safe Mode" (not Reset)

Any difference?

No change.

If you check the certificate for this forum in IE, does the issuer or certificate path vary from the attached? If so, what differences do you notice?

I'm sorry. I don't understand.

I think you are using this forum in Internet Explorer. True?

On the address bar there should be a padlock icon you can click and then View Certificate for this site.

Please compare what you see in the certificate viewer with the screen shot in my post.

Do you see a difference there?

I am indeed in IE. I can check the certificate through the padlock. However, I don't know where to find it in the screen shot in your post. Thanks.

When you click the lock on your address bar and choose View Certificate (or View Certificates) you should get a dialog with several tabs. Can you open the dialog and find the Details tab?

Assuming you can find the Details tab, who is the Issuer?

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