readit - 6:25 pm on Sep 28, 2012 (gmt 0)
Yes, the prefixes made it work. I am aware of the fact that the standard is not fixed yet and that the box-attribute has been replaced by (temporarily "flexbox" and now by) "flex".
You are also right that firebug doesn't report the flexbox code as an error, it simply ignores it for me. Chromium however points it out.