Secure Socket Layer, or SSL, protects private data by encrypting it during transmission. To enable SSL encryption, websites use an SSL certificate issued by a certificate authority. When you enter an "https://" address to browse a site, Firefox checks the SSL certificate data to determine whether it is valid. When Firefox encounters an expired or invalid SSL certificate, it blocks the page or displays a warning. However, you might want to disable the warnings or blocking of unencrypted sites for site testing or other reasons. A change to advanced Firefox preferences allows you to prevent the warnings.
Type "about:config" in the address bar and press the "Enter" key. When prompted with the "This might void your warranty!" warning message about changing advanced settings, click the "I'll be careful, I promise!" button.
Type "browser.ssl_override_behavior" in the "Filter" box. Double-click the "browser.ssl_override_behavior" value in the "Preference Name" list.
Change the value in the "Enter integer value" dialog box from "2" to "1" and click the "OK" button.
Close the browser and restart it. Firefox no longer blocks access to sites or displays warnings because of invalid SSL certificates.