When stereoscopic warping is applied for a WebVR fullscreen container (i.e. using an Oculus VR headset), child elements that do not intersect with the bottom-right quadrant of the viewport will disappear at certain angles. This often happens when using a very large box of CSS transformed elements as a sky box.

This issue is independent of the clipping issues that occurred when elements were partly in front and behind, as it only occurs when stereoscopic rendering for CSS transformed elements is applied in WebVR.

The CSS VR code that caused this bug was in the "Larch" branch, and will not be landed as-is in mozilla-central. With the WebVR 1.0 API, there will be a new way to send HTML elements to the stereoscopic display, by extending the VRLayer dictionaries passed into "VRDisplay.RequestPresent". Details on the WebVR 1.0 API are here: https://mozvr.github.io/webvr-spec/