Pseudo element with paint() background not rendering in Firefox

[jsnkuhn]

Pseudo element with paint() not rendering in Firefox

https://codepen.io/jsnkuhn/pen/NWgBBdO?editors=0100

the third example in this pen (the one with the text "Hover Me" and .example-4) has a paint() background image attached to a :before pseudo element. This renders in chrome without the polyfill but in Firefox with the polyfill no dice

FYI, already checked to make sure -moz-element() works on pseudo-elements in FF and yes it does so that isn't the problem

https://codepen.io/jsnkuhn/pen/QWQxKNb?editors=1100