Firefox uses certificates on secure web sites (those that start with https:) to ensure that your information is being sent to the intended recipient and can't be read by eavesdroppers. To keep you secure, Firefox will warn you if there's a problem with a site's certificate. Note that these warnings don't mean that you currently have a security problem; they just mean that you could have one if you access the site they block.

This article will describe some of the common warnings you can receive with the heading Secure Connection Failed. If you don't see this heading, see Las páginas no se cargan - resolver problemas y solucionar los mensajes de error.

Certificate is only valid for (site name)

This error is telling you that the certificate sent to you by the site is actually for another site. While anything you send would be safe from eavesdroppers, the recipient may not be who you think it is.

A common situation is when the certificate is actually for a different part of the same site. For example, you may have visited https://example.com, but the certificate is for https://www.example.com. In this case, if you access https://www.example.com directly, you should not receive the warning.

The certificate is not trusted because it is self signed

Self-signed certificates make your data safe from eavesdroppers, but say nothing about who the recipient of the data is. This is common for intranet web sites that aren't available publicly.

Bypassing the warning

You can tell Firefox to bypass these warnings. You should only bypass the warning if you're sure that the site is legitimate. Legitimate public sites will not ask you to do this. An invalid certificate can be an indication of a web page that will defraud you or steal your identity.

1. On the warning page, click Or you can add an exception....
2. Click Add Exception.... The Add Security Exception dialog will appear.
3. Click Get Certificate.
4. Read the text describing the problems with this site.
5. Click Confirm Security Exception if you want to trust the site.

The certificate contains the same serial number as another certificate

This error alerts you to the fact that the certificate the page you're visiting uses has a serial number identical to one you've already accepted. This warning cannot be bypassed using the method above. For more information and for instructions on how to work around this message, see the El certificado contiene el mismo número de serie que otro certificado article.