CertAlert by Neha Olsen

CertAlert is an essential Firefox extension that actively monitors website certificates for you. It displays the number of days left until the certificate expires on a padlock icon in the toolbar, keeping you informed and proactive.

When there are fewer than 29 days left, the icon turns red to draw your attention. Additionally, if the site connection is not encrypted, it shows an unlocked red padlock, signaling potential security vulnerabilities.