When deploying a TLS enabled website, you must ensure that all content loaded on the site is loaded from secure origin. If your content is loaded from an insecure source, the security of your whole site is compromised and modern browsers will downgrade your website’s security rating.
The HTTPS Mixed Content Detector plugin attempts to identify sources of mixed content warnings. The plugin will examine content loaded from the site when admins are viewing the site. Any content that violates the policy of loading content that originates from “https:” resources will trigger an error and that resource will be logged. Viewing the log will allow you to examine the site for any warnings and remove them before they cause problems for your website.