backface-visibility

Summary

Determines whether or not the “back” side of a transformed element is visible when facing the viewer.

visible: The back face of an element is a transparent background, displaying a mirror image of the front face when the back face is observable.
hidden: There are cases when we do not want the front face of an element to be visible through the back face, like when doing a flipping card effect (setting two elements side-to-side). In this case, the property should be set to hidden to make the back face of the element opaque.

backface-visibility: visible;

backface-visibility: hidden;

This property disables position: fixed on Firefox, see related bug: https://bugzilla.mozilla.org/show_bug.cgi?id=876341