Well, here's why!
Firefox added blocking of active content in recent versions (from version 23.0 and onwards). This happens when you try to use the site while browsing securely via https
"Firefox has blocked content that is insecure on the page you're visiting". This actively makes it impossible to upload new deviations.
Stupid that it hasn't been fixed yet. It's been several months now that this site has been broken!developer.mozilla.org/en-US/do…