hello, first please make sure that the date, time & timezone are set correctly on your system. if this doesn't solve the issue (or it is already set properly), a possible solution depends on different factors:

• what is the error code shown under technical details on the error page?

in case the error code equals sec_error_unknown_issuer, please attempt to add an exception on the bottom of the error page & inspect the certificate (see the screenshot attached for instructions):

• which issuer information does the certificate contain?

thank you!

"This Connection is Untrusted" error message appears - What to do

Hi Nigel, because the security error message can be caused by malware, or a configuration issue with your security software, could you check those exceptions and see whether we can spot the reason that the certificates were not accepted?

When on a site where you saved an exception, click the padlock icon in the address bar > More Information > View Certificate. Then check the "Issued by" section to see who is listed there.

As examples, I have attached what I get for this site today, and what I got for google.com last Monday.

Phillip, The problem with Gmail in particular is that there is no "I Understand the Risks" for me to select! The system date and time are fine. It was all working fine before I applied the update to another program.

Jscher2000 I will run a scan and check for malware etc.

Thanks Nigel

Hi Nigel, it still would be helpful to know what you are seeing when checking the certificates for sites where you were able to make exceptions. Sometimes leads to a very quick and direct solution.

What is the other program you speak of?

I am able to get to some other sites that I want and I already made the exception to get to google.com. I have attached the screen from the gmail block which I can't get around. I also now get "Uh-oh, something went wrong! Error Code: 404 " from some major commercial sites - which I'm sure wouldn't use such a phrase!

Thanks Nigel

Fred It was Vuze, a torrent client. I was prompted to upgrade to 5.4.0.0 and it closed Firefox and when I restarted the browser all this happened.

Thanks Nigel P.S. Vuze had no reason to close Firefox that I could see - it didn't close IE.

Are you using Kaspersky Internet Security? I had to clear KIS scanning of encrypted connections.

Navigation: Open KIS Settings Additional Network Settings Clear/uncheck "Scan encrypted connections"

If you don't have KIS, sorry to bomb your thread.

No, but thanks anyway.

Nigel

Open your add-ons manager. Disable a few add-ons, then Restart Firefox. If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is detective.

You can also try to reset the router.

Hi Nigel, I understand that you made some exceptions, but my point is, who is the issuer of the certificates that Firefox found invalid? Please check, or it is impossible to get to the root of the problem. See: https://support.mozilla.org/questions/1015931#answer-617103

Thanks to all. On restarting the PC last night I found the problem has disappeared! I rebooted a couple of times before but that had made no difference. I appreciate your help.

Nigel

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.