Closes https://github.com/TryGhost/Casper/issues/330
As usual Firefox is the bane of fucking everything and despite IE7 calling multiple times wanting its rendering back, here we are. Responsive video embeds insider a flexbox element do not work in Firefox and require an additional (very specific) wrapping div. I've adjusted the Fitvids.js script here to include that div in its injection along with the requisite styles. It's a horrible hack. Spent 2 hours trying to find another way but I cant.
