You are seeing Bug 716524 - 'perspective' only affects child nodes, not further descendants. The defect describes that there is a difference between Chrome and Firefox in their interpretation of what inherited means. It looks like it should not be inherited, according to perspective
MDN documentation but I sort of agree with Chrome as it feels intuitive to propagate it to descendants.
I tried the workaround from 3D transformations with Firefox 10+ which recommends reapplying transform-style: preserve-3d
(with or without the -moz-
depending on which versions of Firefox you care about supporting) at each depth but that still wasn't working for me.
Moving perspective
and perspective-origin
to the <ul>
fixes the problem in Firefox.