Since Twitter and Facebook are well-run sites that should NOT need an exception, I would like to assist you in investigating the source of this issue.

Are Twitter and Facebook the only sites where you have seen a certificate error and need to make an exception? Have you already saved exceptions for this site or any other site?

What is the error code in the page? Typically that looks like one of the following:

• sec_error_bad_signature
• sec_error_unknown_issuer

Sometimes the code mentions a date issue or something else, so please let us know the specific code.

Also, do you use Avast, BitDefender, ESET or Kaspersky security software?

ThanX for reply as i am a new computer user so i dont have much idea of thingd. I am just a month old in using my own laptop. The error page shows sec_error_unknown_issuer as error code while clicking in Technical details. I dont use Avast, BitDefender, ESET or Kaspersky security software. Dont even know about any one of them & yes this problem is only in twitter and facebook. Even google, youtube all are runnibg properly

I'm assuming you can access Twitter and Facebook using another browser such as Internet Explorer. Could you inspect the site's certificate information in IE? To do that, load the site then click the padlock in the address bar. One of the options should be to view the certificate. If you are using Google Chrome for the test, first click Connection and then you can view the certificate.

I want to know what is listed in the "Issued by" and "Certificate Path" information for Twitter and Facebook. I have attached an example of what I see for Twitter on the first, second, and third tabs of that dialog. What do you see?

If you can't inspect the certificate via "I Understand the Risks" then try this:

Open the "Add Security Exception" window by pasting this chrome URL in the Firefox location/address bar and check the certificate:

• chrome://pippki/content/exceptionDialog.xul

In the location field of this window type or paste the URL of the website.

• retrieve the certificate via the "Get certificate" button
• click the "View..." button to inspect the certificate in the Certificate Viewer

You can inspect details like the issuer and the certificate chain in the Details tab of the Certificate Viewer. Check who is the issuer of the certificate. If necessary then you can attach a screenshot that shows the certificate viewer.

This problem is still not solved When i try to see the issuer of certificate this comes

FortiGate sounds like an enterprise security device... searching...

Fortinet has a document on how to import the FortiGate signing certificate into Firefox so that you can trust the proxy, but since IT needs to take the first set of steps, I don't know whether this is useful for you:

http://docs.fortinet.com/uploaded/files/1963/Preventing-security-certificate-warnings.pdf

I've the same problem, this is the screenshot. How can i fix that?

Hi Jefry, can you start at the top of this discussion and see whether you can identify a particular program or device that is intercepting your secure connections?

If you want personal assistance, please start a new question and include your system information:

https://support.mozilla.org/questions/new/desktop/fix-problems

Scroll down past suggested articles to continue entering your question.