在FF之后，宽度转换不起作用

I have this menu that I want to try some new animation with on the hover state. The problem is that the width transition doesn't seem to work in Firefox, but in Chrome, Safari and IE. I've tried with both Bourbon mixin and without, no help. Is Firefox not capable of having CSS transitions on pseudo elements or what could cause the problem?I have this menu that I want to try some new an