Why am I suddenly getting a “Blocked loading mixed active content” issue in Firefox?

This morning, upon upgrading my Firefox browser to the latest version (from 22 to 23), some of the key aspects of my back office (website) stopped working. Looking at the Firebug log, the following errors were being reported: Blocked loading mixed active content “http://code.jquery.com/ui/1.8.10/themes/smoothness/jquery-ui.css” Blocked loading mixed active content “http://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.10/jquery-ui.min.js”` among other errors caused by … Read more