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.
It means you're calling http from https. You can use src="//url.to/script.js" in your script tag and it will auto-detect.
Alternately you can use use https in your src even if you will be publishing it to a http page. This will avoid the potential issue mentioned in the comments.