Why CSS3 perspective is not working in firefox

Question

I am trying to create a 3d flipcard . But perspective property is not working in firefox v21 .

see the code http://codepen.io/prantor19/pen/cgoKm

can you explain why?

Answer 1

you forgot px after perspective value!!

like this:

  -webkit-perspective:600px;
  -moz-perspective:600px;
  perspective:600px;