Site Information panel
The Site Information panel is where you can view information about a website’s connection security and identity.
Connection security
A padlock icon 
in the address bar will indicate whether the connection to the website is fully secure. For more information, click the padlock to open the Site Information panel. This panel shows you whether the current connection is classified as secure.
Click the right arrow in the Site Information panel to view the Connection Security panel. This is where you can learn more about connection security, such as the issuer of a certificate for a secure connection and – if it is made available – the website’s owner, or disable the blocking of insecure content on a site. This panel also includes a More Information button that will open the Page Info window Security tab for the website.
See How do I tell if my connection to a website is secure? to learn more about connection security. The Mixed content blocking in Waterfox article tells you about Waterfox’s content blocking security feature.