Firefox Community Forum

In the last few months, FireFox (accesed from Roamnia, on Firefox an a MacOS 26, both always updated to the latest available final version) has been showing the error: “Be careful. Something doesn’t look right. Firefox spotted a potentially serious security issue with e360.yale.edu. 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? 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 it looks like the certificate expired on 14/08/2026. What can you do about it? Your device’s clock is set to 22/09/2026. If this is correct, the security issue is probably with the site itself. If it’s wrong, you can change it in your device’s system settings. View the site’s certificate Learn more about troubleshooting time-related errors Error Code: SEC_ERROR_EXPIRED_CERTIFICATE 22 Sept 2026 08:34:11 EEST“ On perfectly innocent sites. Two examples: FAIR.org does not load beyond the initial “Home” page; e360.yale.edu/ shows the warning instead of accessing the homepage. This is annying, possibly wrong and, as any false security warning, potentially dangerous. Please help.

I'm reposting a question already opened here because a moderator suggested to do so. Actually I though I was posting to the international forum from the URL...

I was trying to access a local HTTPS website of an embedded device (a Siemens S7-1500 PLC) that is using a self-signed certificate, but was unable to go on (attached image #1, in Italian language) due to the the SEC_ERROR_REUSED_ISSUER_AND_SERIAL error. I've browsed a similar PLC webserver in the past, so the fact that the device exposes a similar certificate serial number is not so strange for me, considering also it's self-signed.

The problem is that I cannot follow the instructions of the Mozilla knowledgebase here because I'm not able to identify the correct certificate of the website!

In the attached image #2 you can see that the connection is detected as not encrypted, I suppose because only the form part of the HTML that is posting the data using HTTPS while the rest is using HTTP, but I'm not sure. If I click on the padlock icon (attached image #3) the info about the current certificate is not displayed.

Then I went into Tools > Options and searched for "certificates"; as you can see in the attached images #4 and #5, neither in the Servers tab nor in the Authorities tab I can find any item that is related to 192.168.10.2 (the webserver IP address) or Siemens (the embedded device manufacturer). But unfortunately the error persist! Initially there was a 192.168.10.2:443 line in the Servers tab and I removed it and restarted Firefox, but it didn't solve, so at the moment the situation is the one depicted by the attachments.

I had to use Microsoft Edge to access the website, but I would like to solve this issue and use Firefox instead. Is there anything else I can do to bypass the error? Why doesn't the error page provide a way to correctly identify the wrong certificate using its fingerprint and/or name? Or, maybe, is there a way to disable this check for local IP addresses or for items in a whitelist?

Thanks for your help.

I am continually getting this error message,I can't get rid of this and I'm about to ghange browsers. Secure Connection Failed 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? The issue is most likely with the website, and there is nothing you can do to resolve it. You can notify the website’s administrator about the problem. Error Code: PR_END_OF_FILE_ERROR

https://www.optimist.com/ip

Peer’s Certificate issuer is not recognized.

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

Certificate chain:

MIIHoDCCBYigAwIBAgIQCdfAXF6McwVTRnHF1rN+hzANBgkqhkiG9w0BAQsFADBc MQswCQYDVQQGEwJVUzEXMBUGA1UEChMORGlnaUNlcnQsIEluYy4xNDAyBgNVBAMT K1JhcGlkU1NMIEdsb2JhbCBUTFMgUlNBNDA5NiBTSEEyNTYgMjAyMiBDQTEwHhcN MjIwNzIwMDAwMDAwWhcNMjMwNzIwMjM1OTU5WjAcMRowGAYDVQQDDBEqLnlvdXJw c2VydmVyLm5ldDCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAKnQxr4J f7cwlg36FGdNBi91Ks7oiCTMEHbeIeMlVjI4xVhZgH/bF/7jxYXIWQJndIyz+TNK ut5IiQiG6Kimf2YZfO6skNyDADP0+dvPb2pZ0/TIwBNWfeVQQDjqyF1ypx4Y4CBn yw22D4ObLJG8qnm0KKhModRfhM1N1m+kVknul/TEyErSyJt1KoOk/cF0tX5GQhfZ dIjLvTpUz3qlP9f4f5vEFEo7dd9m0vwDYv3qXMXcmgKxhUM7QJ33V859/nM/2ZaR VWb7CCjlG77AySIs6f9hHEup/DOFepT/9+KUi84Tb3//ZNaLOjpq4nbNTNoMvtol eUL8HykQFvNr8/8CAwEAAaOCA5wwggOYMB8GA1UdIwQYMBaAFPCchf2in32PyWi7 1dSJTR2+05D/MB0GA1UdDgQWBBSfaa2w6EGfzgotCCoF+kBDWuSTOjAtBgNVHREE JjAkghEqLnlvdXJwc2VydmVyLm5ldIIPeW91cnBzZXJ2ZXIubmV0MA4GA1UdDwEB /wQEAwIFoDAdBgNVHSUEFjAUBggrBgEFBQcDAQYIKwYBBQUHAwIwgZ8GA1UdHwSB lzCBlDBIoEagRIZCaHR0cDovL2NybDMuZGlnaWNlcnQuY29tL1JhcGlkU1NMR2xv YmFsVExTUlNBNDA5NlNIQTI1NjIwMjJDQTEuY3JsMEigRqBEhkJodHRwOi8vY3Js NC5kaWdpY2VydC5jb20vUmFwaWRTU0xHbG9iYWxUTFNSU0E0MDk2U0hBMjU2MjAy MkNBMS5jcmwwPgYDVR0gBDcwNTAzBgZngQwBAgEwKTAnBggrBgEFBQcCARYbaHR0 cDovL3d3dy5kaWdpY2VydC5jb20vQ1BTMIGHBggrBgEFBQcBAQR7MHkwJAYIKwYB BQUHMAGGGGh0dHA6Ly9vY3NwLmRpZ2ljZXJ0LmNvbTBRBggrBgEFBQcwAoZFaHR0 cDovL2NhY2VydHMuZGlnaWNlcnQuY29tL1JhcGlkU1NMR2xvYmFsVExTUlNBNDA5 NlNIQTI1NjIwMjJDQTEuY3J0MAkGA1UdEwQCMAAwggF/BgorBgEEAdZ5AgQCBIIB bwSCAWsBaQB3AOg+0No+9QY1MudXKLyJa8kD08vREWvs62nhd31tBr1uAAABghul OY0AAAQDAEgwRgIhAJbuqeZ9f8Ac6m50ILPUpUqTKinFzYbRUIN6KYvv9F2CAiEA xyBVuQCJAKgeZejxYW00DqJheKhxKiex3AK1IKlEKTgAdgA1zxkbv7FsV78PrUxt Qsu7ticgJlHqP+Eq76gDwzvWTAAAAYIbpTl2AAAEAwBHMEUCICjQIOEO9nB8mlrn WEtwenhFZNjXPv59aAUubvAD/ODkAiEAouy0zbUHZH+EMaga0+SoRfTepye5ZRST l+lyLZhOZpAAdgCzc3cH4YRQ+GOG1gWp3BEJSnktsWcMC4fc8AMOeTalmgAAAYIb pTmdAAAEAwBHMEUCIQD7EICYFxdSLjmFYqtvgQ6SJNf6d2RdtevPD1LDJL0z7wIg bj1JbkqD8NM30V/mNLaetglFEIOoah8htgJhUCzKh+gwDQYJKoZIhvcNAQELBQAD ggIBAHI1arifGFsXip7Ts5nuTY/wdBaHzP9apsdvEqDIr+dUeCaslAT5kXQapYY7 5MwWDWnO6f4f7yyacnFXcrQ6Ra6fpB7ps0X5dN4iVhhe+Nq0MN+M1Q/+Ui3a67FC D8NznIVP5WjKmEj1Be2vR41hleFXB5ILckUf+M16MtzQZYQkGXaj8uf+FxD++Dl4 jUfWEdOeFM4ODgzETaXpBHSxoqBohq7YYr4r6M5P42uFm6CVcLYmc2y/+R3eAyny PMpvA7WVnun8fW3MFCWZs6TDIlAOfpDIEXT5eOtcrZM9NiNqjSeoTMElAJyC4TSX Q5K3DI9JxDT9wQDtxvjAVuax7EoULShUkEjUX2ojKjOwXJpLINokwaILqN9/jQFj mqK8Mm0biyMH281O2X2Gkbt7qyradza2EjcQA3pFeaEsEdxi6+tbTPlFdK8/l8l5 8VMNx/hYaHXRjJLMHEj3Uwh7Bdh2w3KcdDszrqQWy12C4osA4k3IhpNrT5dOePj9 9ODYgMI4k2oTOHAlvXo6fjSE6yXhPdqbBQ2hs88OqJc5A5cE2lYZgY+bE9EDpXn7 B/lhtiLY3TgLflRawa00FCoWZBkBnQL+L1hY1w/taRd1hT3bmz8QmN0AhxR8HmSZ 2Jbv6tcYGufmWapQ8tO+kFXpsHTN6KBEaYH+F30hDidG6ZJY

MIIFyzCCBLOgAwIBAgIQCgWbJfVLPYeUzGYxR3U4ozANBgkqhkiG9w0BAQsFADBh MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3 d3cuZGlnaWNlcnQuY29tMSAwHgYDVQQDExdEaWdpQ2VydCBHbG9iYWwgUm9vdCBD QTAeFw0yMjA1MDQwMDAwMDBaFw0zMTExMDkyMzU5NTlaMFwxCzAJBgNVBAYTAlVT MRcwFQYDVQQKEw5EaWdpQ2VydCwgSW5jLjE0MDIGA1UEAxMrUmFwaWRTU0wgR2xv YmFsIFRMUyBSU0E0MDk2IFNIQTI1NiAyMDIyIENBMTCCAiIwDQYJKoZIhvcNAQEB BQADggIPADCCAgoCggIBAKY5PJhwCX2UyBb1nelu9APen53D5+C40T+BOZfSFaB0 v0WJM3BGMsuiHZX2IHtwnjUhLL25d8tgLASaUNHCBNKKUlUGRXGztuDIeXb48d64 k7Gk7u7mMRSrj+yuLSWOKnK6OGKe9+s6oaVIjHXY+QX8p2I2S3uew0bW3BFpkeAr LBCU25iqeaoLEOGIa09DVojd3qc/RKqr4P11173R+7Ub05YYhuIcSv8e0d7qN1sO 1+lfoNMVfV9WcqPABmOasNJ+ol0hAC2PTgRLy/VZo1L0HRMr6j8cbR7q0nKwdbn4 Ar+ZMgCgCcG9zCMFsuXYl/rqobiyV+8U37dDScAebZTIF/xPEvHcmGi3xxH6g+dT CjetOjJx8sdXUHKXGXC9ka33q7EzQIYlZISF7EkbT5dZHsO2DOMVLBdP1N1oUp0/ 1f6fc8uTDduELoKBRzTTZ6OOBVHeZyFZMMdi6tA5s/jxmb74lqH1+jQ6nTU2/Mma hGNxUuJpyhUHezgBA6sto5lNeyqc+3Cr5ehFQzUuwNsJaWbDdQk1v7lqRaqOlYjn iomOl36J5txTs0wL7etCeMRfyPsmc+8HmH77IYVMUOcPJb+0gNuSmAkvf5QXbgPI Zursn/UYnP9obhNbHc/9LYdQkB7CXyX9mPexnDNO7pggNA2jpbEarLmZGi4grMmf AgMBAAGjggGCMIIBfjASBgNVHRMBAf8ECDAGAQH/AgEAMB0GA1UdDgQWBBTwnIX9 op99j8lou9XUiU0dvtOQ/zAfBgNVHSMEGDAWgBQD3lA1VtFMu2bwo+IbG8OXsj3R VTAOBgNVHQ8BAf8EBAMCAYYwHQYDVR0lBBYwFAYIKwYBBQUHAwEGCCsGAQUFBwMC MHYGCCsGAQUFBwEBBGowaDAkBggrBgEFBQcwAYYYaHR0cDovL29jc3AuZGlnaWNl cnQuY29tMEAGCCsGAQUFBzAChjRodHRwOi8vY2FjZXJ0cy5kaWdpY2VydC5jb20v RGlnaUNlcnRHbG9iYWxSb290Q0EuY3J0MEIGA1UdHwQ7MDkwN6A1oDOGMWh0dHA6 Ly9jcmwzLmRpZ2ljZXJ0LmNvbS9EaWdpQ2VydEdsb2JhbFJvb3RDQS5jcmwwPQYD VR0gBDYwNDALBglghkgBhv1sAgEwBwYFZ4EMAQEwCAYGZ4EMAQIBMAgGBmeBDAEC AjAIBgZngQwBAgMwDQYJKoZIhvcNAQELBQADggEBAAfjh/s1f5dDdfm0sNm74/dW MbbsxfYV1LoTpFt+3MSUWvSbiPQfUkoV57b5rutRJvnPP9mSlpFwcZ3e1nSUbi2o ITGA7RCOj23I1F4zk0YJm42qAwJIqOVenR3XtyQ2VR82qhC6xslxtNf7f2Ndx2G7 Mem4wpFhyPDT2P6UJ2MnrD+FC//ZKH5/ERo96ghz8VqNlmL5RXo8Ks9rMr/Ad9xw Y4hyRvAz5920myUffwdUqc0SvPlFnahsZg15uT5HkK48tHR0TLuLH8aRpzh4KJ/Y p0sARNb+9i1R4Fg5zPNvHs2BbIve0vkwxAy+R4727qYzl3027w9jEFC6HMXRaDc=

MIIDrzCCApegAwIBAgIQCDvgVpBCRrGhdWrJWZHHSjANBgkqhkiG9w0BAQUFADBh MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3 d3cuZGlnaWNlcnQuY29tMSAwHgYDVQQDExdEaWdpQ2VydCBHbG9iYWwgUm9vdCBD QTAeFw0wNjExMTAwMDAwMDBaFw0zMTExMTAwMDAwMDBaMGExCzAJBgNVBAYTAlVT MRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5j b20xIDAeBgNVBAMTF0RpZ2lDZXJ0IEdsb2JhbCBSb290IENBMIIBIjANBgkqhkiG 9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4jvhEXLeqKTTo1eqUKKPC3eQyaKl7hLOllsB CSDMAZOnTjC3U/dDxGkAV53ijSLdhwZAAIEJzs4bg7/fzTtxRuLWZscFs3YnFo97 nh6Vfe63SKMI2tavegw5BmV/Sl0fvBf4q77uKNd0f3p4mVmFaG5cIzJLv07A6Fpt 43C/dxC//AH2hdmoRBBYMql1GNXRor5H4idq9Joz+EkIYIvUX7Q6hL+hqkpMfT7P T19sdl6gSzeRntwi5m3OFBqOasv+zbMUZBfHWymeMr/y7vrTC0LUq7dBMtoM1O/4 gdW7jVg/tRvoSSiicNoxBN33shbyTApOB6jtSj1etX+jkMOvJwIDAQABo2MwYTAO BgNVHQ8BAf8EBAMCAYYwDwYDVR0TAQH/BAUwAwEB/zAdBgNVHQ4EFgQUA95QNVbR TLtm8KPiGxvDl7I90VUwHwYDVR0jBBgwFoAUA95QNVbRTLtm8KPiGxvDl7I90VUw DQYJKoZIhvcNAQEFBQADggEBAMucN6pIExIK+t1EnE9SsPTfrgT1eXkIoyQY/Esr hMAtudXH/vTBH1jLuG2cenTnmCmrEbXjcKChzUyImZOMkXDiqw8cvpOp/2PV5Adg 06O/nVsJ8dWO41P0jmP6P6fbtGbfYmbW0W5BjfIttep3Sp+dWOIrWcBAI+0tKIJF PnlUkiaY4IBIqDfv8NZ5YBberOgOzW6sRBc4L0na4UU+Krk2U886UAb3LujEV0ls YSEY1QSteDwsOoBrp+uvFRTp2InBuThs4pFsiv9kuXclVzDAGySj4dzp30d8tbQk CAUw7C29C79Fv1C5qfPrmAESrciIxpg0X40KPMbp1ZWVbd4=

I've never had Secure Connection Failed warnings before, but now I am getting them often. I don't want to stop using Firefox, but it seems I can get to these sites via other browsers.

Google stopped working for me in Firefox a couple of weeks ago. Every time I enter something in the Google search bar, I get the following error message:

An error occurred during a connection to misho.sodirant.com. SSL received a record that exceeded the maximum permissible length.

How can I fix this? I have had to switch to Chrome to Google anything. I want to stay with Firefox since all my bookmarks are there.

David Beaverton OR

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.