Sorry, but what kind of system has this issue. The tags on your post refer to Firefox for Android. Is that correct, or is it on a desktop operating system?

It's Windows 8

Thank you for clarifying that.

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.

Of course, the problem also could be caused by spyware.

If you have added Exceptions, 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 the 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 do you see?

moved to desktop Firefox