I had no problem with the link. What is the exact error message?

What security software do you have?

Could you please provide more detail?

• click the "Advanced" button show more detail
• click the blue SEC_ERROR_UNKNOWN_ISSUER message to show the certificate chain
• click "Copy text to clipboard" and paste the base64 certificate chain text in a reply

See also:

• https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

The following is the text error message, I am using Norton antivirus and no other sites appear to be affected.

www.vehicletax.service.gov.uk uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported. Error code: SEC_ERROR_UNKNOWN_ISSUER

FredMcD said

I had no problem with the link. What is the exact error message?

This is the message, I haven't had this problem on any other site at present. www.vehicletax.service.gov.uk uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported. Error code: SEC_ERROR_UNKNOWN_ISSUER

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

http://kb.mozillazine.org/Error_loading_websites

https://www.bing.com/search?q=web+site+access+denied

• uses an invalid security certificate SSL_ERROR_BAD_CERT_DOMAIN
• configured their website improperly

How to troubleshoot the error code "SEC_ERROR_UNKNOWN_ISSUER" on secure websites https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

Do you see a certificate chain if you click SEC_ERROR_UNKNOWN_ISSUER or is nothing shown?

This is a markedly insufficient answer to a problem that seems to be collecting a lot of posts. I would ask the same question, maybe a bit differently, had I not seen it asked half-a-dozen times already. I read ALL the responses, which essentially were non-responsive, and made me suddenly doubt the confidence I had placed in Mozilla for years. The response is strangely diffident and offers a solution that smacks of Amateur Coding Hour. The race car driver doesn't have to be an under-the-hood mechanic to drive the car. That's someone else's purview (obviously.)

For the sake of clarity: I ran Firefox all day today with no problem. As I do web design I thought it prudent to install the developer's version and being on that page interested me in the Nightfall dealy, so I got that, too. I install them both, and now I'm getting this error message on MY OWN SITE. I set it as my homepage, and Firefox refused to open it. It's on Network Solutions, and I do have certificates that are VALID on the thing with a valid https address. EDGE managed to open it for most of this year. Firefox had no complaint yesterday and most of today.

It's just when I installed those two alternative browsers that suddenly Firefox doesn't want to open any site - and I even (just for grins) hit the U.S. Government's Internal Revenue Service (IRS) and Firefox claimed even THEY were suspect, and refused to open that site.

No I have NONE of the listed virus packages. I have Norton and that doesn't matter ANYWAY as everything was working just fine until....now your support page is having me troubleshoot this thing. It's YOUR software that did it. Answer Please.

EDIT: OMG, I was poking around "My Questions" to find I had asked a question here before, two years ago. Guess what...it was about this same THING! And, guess another what...I got the Avast response then....then the click this, check that, find this, erase that. Then it made no sense. Now it makes no sense. A browser that works fine one minute, on a page, suddenly doesn't work at all on the same page? You're not going to find this on any files on my drive. Nada.

EDIT EDIT: Oh yeah. One last thing. I uninstalled Firefox. Sure. I might be able to cobble together some fix. But, I stopped torturously working around things when I upgraded Win95. Mozilla, do something about this. IF I see an official post on this saying the devs found it and fixed it, I may reinstall. Until then, not many of my friends are going to hear me say, "Yeah. I use Firefox. It's great." I'm not going to hold my breath. Don't worry. Nice site, by the way. I like the pretty blue.

EDIT EDIT EDIT: It just occurred to me. Firefox is telling its users my website isn't safe. According to Network Solutions it meets all security requirements. According to Firefox, Networks Solutions, and therefore MY server is configured incorrectly. I'd like to see Mozilla approach Network Solutions and tell them their servers are configured incorrectly, then publish a transcript of that meeting on this site.