Running the latest version of Firefox.
Just used Flexbox for the first time.
Made a containing div of 1200px flexible.
Added 3 div blocks and in each of them placed an equally sized image.
They spaced out perfectly and on publishing it all looks great in Chrome, Safari and Opera but on Firefox...
The images burst out of the container and disappear off the screen. I re-created the problem on another site and it did exactly the same.