The Mixed Content Blocker we described last month is now available in Firefox Beta and is on track for a general release in August with Firefox 23. When secure HTTPS pages load additional content insecurely over HTTP, users are vulnerable to man-in-the-middle and eavesdropping attacks. The feature will block insecure active content by default, protecting our users from these attacks. If you find a website that isnt functioning correctly because it contains insecure content that is being blocked, please let us know by sending an email to [email protected] or commenting in our compatibility tracking bug.”]
Source: https://blog.mozilla.org/security/2013/06/27/mixed-content-blocker-hits-firefox-beta/