Firefox invalid security certificate error

Written by NickWal

(Error code: sec_error_untrusted_issuer)

Using the default settings, when you connect using Firefox to a site which is using an invalid SSL certificate. You will receive a warning like this.

Firefox Invalid Security Certificate

If you know the site, and really wish to proceed you have the option of adding an exception so that while this site continues to use this invalid certificate you will be able to visit it.

Recently my own copy of Firefox stopped showing this friendly page, and started showing this alert instead.

Invalid Certificate Error

The only way to add an exception seemed to be buried deeply in the options, and was extremely inconvenient to use. At first I blamed a recent update to Firefox and wondered if security had been tightened up for some reason. However later I realized I was in fact to blame. A setting I had altered recently had been responsible for this behavior. I do a certain amount of web site development and had recently been trying to understand a problem in a website. To that end, in order to see the real content output by the website when it was returning an error. I had turned of the friendly error reporting. It was this change that had upset in the in-line handling and adding of exceptions of SSL pages. So if you have done it yourself but forgotten how, or didn’t realize the side effect, or someone else changed the setting for you. Here is how to fix it:

Go to the browser url window and type:


Then in the filter control type in:


You will see that it is set to false, double click on it to set it to true, and you should get your normal SSL functionality back again.

Good luck!