[mintplant]

Note that if you have, say, HTTPS Everywhere installed, the embedded JSFiddles won't display. The site the post is hosted on supports HTTPS, while JSFiddle apparently does not, so Firefox blocks "loading mixed active content".

[azakai]

I get that on Firefox Nightly with no extensions installed.

[agumonkey]

Same here, https:// or http:// no luck

[qoo]

Mixed Active Content is now blocked by default in Firefox >= 23

https://blog.mozilla.org/tanvi/2013/04/10/mixed-content-bloc...