CSS perspective bug under firefox

I am having issues with the css "transform" property under firefox ( latest version + other versions tested )

Here is the transform applied :

  -moz-transform: perspective(2rem) rotateX(15deg) scaleY(1);
  -o-transform: perspective(2rem) rotateX(15deg) scaleY(1);
  -ms-transform: perspective(2rem) rotateX(15deg) scaleY(1);
  -webkit-transform: perspective(2rem) rotateX(15deg) scaleY(1);
  transform: perspective(2rem) rotateX(15deg) scaleY(1);

And the active element should have

  -moz-transform: perspective(0rem) rotateX(15deg) scaleY(1);
  -o-transform: perspective(0rem) rotateX(15deg) scaleY(1);
  -ms-transform: perspective(0rem) rotateX(15deg) scaleY(1);
  -webkit-transform: perspective(0rem) rotateX(15deg) scaleY(1);
  transform: perspective(0rem) rotateX(15deg) scaleY(1);

Here is a JSfiddle to test under chrome, and under firefox. The "active" element does get a perspective change under chrome & others, while on firefox, it is not replaced.

JSFiddle

I searched for a similar case but it doesn't seem to have occured to someone else.