display: flex - not working in firefox 21

Question

According to this article, the display:flex property should work without any prefix in firefox 21. But, even if I use -moz- before the value, it is

Answer 1

display: flex is currently only supported behind a runtime flag in Firefox.

To enable it, enter about:config in the url field, search for flexbox, and set it to true.

It is enabled by default in Firefox Nightly, as it is a non-stable version.

It is due to be enabled by default in Firefox 22, providing the feature is ready to ship.