Forum der Gemeinschaft Firefox

Hello Mozilla Community,

We are experiencing an issue where our legal services web portal (hdclaims.co.uk) fails to load properly specifically for users on the latest version of Firefox on desktop.

Problem / Issue:

Users report receiving a SEC_ERROR_UNKNOWN_ISSUER error when attempting to access our online claims form.

The issue does not occur in Chromium-based browsers, but Firefox blocks the websocket connection required for live chat support.

Environment Details:

Browser: Firefox Desktop (Latest Version)

Website: hdclaims.co.uk

Server Setup: Nginx reverse proxy with LetsEncrypt / Cloudflare SSL certificate.

Steps Taken:

Verified intermediate CA certificates are properly chained on the origin server.

Tested with a fresh Firefox profile (no extensions enabled), but the security warning persists intermittent for UK users.

Checked SSL Labs report, which confirms an A+ grade.

Is there a specific cipher suite requirement or OCSP stapling configuration in Firefox that could cause this intermittent SSL handshake failure on .co.uk domains?

Any insights from the community would be appreciated!

I get several message that: I cannot connect to Amazon, Several websites, etc. It sometimes has something to do with private windows and/or can't connect! Could be license, ssl, etc. When I force a firefox private window, it works for a while then goes back to the same thing. Any ideas how I can fix this?

Доброго времени суток.

Я установил сертификаты по инструкции, которая лежит на s.sber.ru/70VQ2B . После этого не прогружается полностью окно входа на online.sberbank.ru (не видно содержимого фреймов). Проблема полностью аналогична описанной здесь: https://support.mozilla.org/ru/questions/1597415

Firefox ESR115.40 (64-разрядный, Windows 7) - страница выглядит, как на скриншоте по ссылке выше.

Установлены скачанные сертификаты в самом браузере, они отображаются в разделе Управление сертификатами -> Центры сертификации. После этого абсолютно ничего не изменилось.

Может, надо еще что-то сделать? Или на Firefox ESR115.40 вообще работать не будет? До перехода на сертификат от Минцифры России проблем не было.

There is seriously something wrong with the way Firefox operates. There is nothing wrong with the following site so why am I seeing this message?

Be careful. Something doesn’t look right.

Firefox spotted a potentially serious security issue with news.sky.com. Someone pretending to be the site could try to steal things like credit card info, passwords, or emails.

news.sky.com has a security policy called HTTP Strict Transport Security (HSTS), which means that Firefox can only connect to it securely. You can’t add an exception to visit this site. Advanced What makes the site look dangerous?

The site is set up to allow only secure connections, but there’s a problem with the site’s certificate. It’s possible that a bad actor is trying to impersonate the site. Sites use certificates issued by a certificate authority to prove they’re really who they say they are. Firefox doesn’t trust this site because its certificate isn’t valid for news.sky.com. The certificate is only valid for: . What can you do about it?

news.sky.com has a security policy called HTTP Strict Transport Security (HSTS), which means that Firefox can only connect to it securely. You can’t add an exception to visit this site.

Secure Connection Failed

An error occurred during a connection to my.amarkets.org. SSL received a record that exceeded the maximum permissible length. Advanced What makes the site look dangerous?

The page you are trying to view cannot be shown because the authenticity of the received data could not be verified. What can you do about it?

Please contact the website owners to inform them of this problem.

Learn more about secure connection failures

Error Code: SSL_ERROR_RX_RECORD_TOO_LONG

I have started receiving a secure connection failed error message for a portal log-in website that worked fine for the past 6-7 months (see attached document). Other people in my group use Firefox and Bitdefender to access the portal and none of them are having this issue.

I originally believed the problem to be my anti-virus (Bitdefender) and worked with them to resolve the problems. After trying various solutions including clearing my cache, using private mode and turning off different components of their software, Bitdefender believes the problem is with my browser setting and not their software. I also tried accessing the portal using Chrome in both regular and incognito modes and cannot access the site which would seem to rule out the problem being a Firefox browser problem but contacting Firefox support seems to be the next logical step.

I have been to the Firefox FAQ and saw similar problems with potential solutions - DNS over HTTPS, TLSKEYLOGGING issues, add-on exceptions - none of which worked. I have the most recent version of Firefox and am running Windows 11 home version.

Sometimes if I hit refresh after receiving the error message, the browser will try to connect and I will get a server time out message. If I keep hitting "try again", sometimes the portal log-in screen will appear and allow me to log-in. The key word is "sometimes" since often I just keep getting the server time out message.

Any ideas for me to try from this forum?

I keep getting: "Your connection may not be private Learn more. The page isn’t redirecting properly Firefox can’t connect to the server at auth.www.abebooks.com." I believe that I followed your instructions, but I'm not sure. I do not understand why "auth." appears in the Mozilla response when I do not type "www.auth.abebooks.com" but simply "www.abebooks.com." Thank you! Claude Gratton

Got this error: Your connection may not be private An app or service may see your encrypted traffic from this site. Learn more

Now I know what may be causing it but you offer no solution.

https://beta.refah-bank.ir/

Peer’s Certificate has been revoked.

HTTP Strict Transport Security: false HTTP Public Key Pinning: false

Certificate chain:

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Since your last update, I can't access amazon anymore without a security warning. I know that my connection is private and secure. The only thing that's actually happening, is that my Browser is interfering with me without cause. Can you please make that stop ?

Firefox is saying that there is a problem with my Xfinity internet & advises me not to log in. This happens only on my mac. Firefox seems to work fine on my i pad & i phone. Safari does not show this warning & they are very strict about internet issues. how do I fix this problem?

Over and over again when I try to open a website I get the notice that says "Secure Connection Failed". I have to restart my laptop and then I can open the website that I tried to access before. I've tried using the suggestions in the forum with no result in solving this problem. I've attached the page that comes up showing the problem.

I am currently unable to access certain websites, particularly banking sites. The following error appears: Secure Connection Failed

An error occurred during the connection to modern.ttbank.ir. The peer's certificate has been revoked.

Error code: SEC_ERROR_REVOKED_CERTIFICATE

   The page you are trying to view cannot be displayed because the authenticity of the received data could not be verified.
   Please contact the website owners to inform them of this issue.

This is happening even though I was able to access this site without any problems until yesterday.

My email is jamek2006@yahoo.co.uk but when I try to Log In I am told the site is insecure and the place for password is blocked.

Kindly assist.

I was going to look at a friend's website that has an SSL-certificate, has had it for years, which has been working all that time. Now Firefox informs me: "Firefox doesn’t trust this site because its certificate isn’t valid for www.wuwei-school.nl. The certificate is only valid for: wuwei-school.nl."

Really? I pretty sure there's nothing wrong with the certificate and I was taught that the "www" component is not important as a prefix for the domain name in a URL. It is just a shorthand code to show that the address is a URL. Can Mozilla fix this issue? Or, at least, explain?

Thanks

Firefox's full message: - - - Be careful. Something doesn’t look right.

Firefox spotted a potentially serious security issue with www.wuwei-school.nl. Someone pretending to be the site could try to steal things like credit card info, passwords, or emails. Advanced What makes the site look dangerous?

The site is set up to allow only secure connections, but there’s a problem with the site’s certificate. It’s possible that a bad actor is trying to impersonate the site. Sites use certificates issued by a certificate authority to prove they’re really who they say they are. Firefox doesn’t trust this site because its certificate isn’t valid for www.wuwei-school.nl. The certificate is only valid for: wuwei-school.nl. What can you do about it?

Probably nothing, since it’s likely there’s a problem with the site itself. Sites use certificates issued by a certificate authority to prove they’re really who they say they are. But if you’re on a corporate network, your support team may have more info. If you’re using antivirus software, try searching for potential conflicts or known issues.

View the site’s certificate

Learn more about secure connection failures

Error Code: SSL_ERROR_BAD_CERT_DOMAIN

Aug 21, 2026 11:10:31 PM GMT+2 - - -

Здравствуйте. Я живу в России и у многих Российских сайтов отозвали сертификаты безопасности, но нам гражданам этой страны приходится пользоваться данными сайтами на свой страх и риск. В последних версиях Firefox не даёт войти на данные сайты даже на свой страх и риск. Прошу Вас от лица всех людей проживающих на территории России вернуть кнопку "принять риск и войти на сайт".

Заранее спасибо.