At ToT as of October 10, another 2D pop-up joins the list.

When in WebVR, using the device volume keys (which are accessible even in the headset) showed:

- The volume adjustment notification pop-up (barely visible at the top of the screen).
- The "high volume can break your ears" warning dialogue (much more central in the field of view).

When adjusting volume with the VR controller, the volume change notification isn't shown.  I'm rebooting to see if the warning shows or not (the notification doesn't show every time).  But either way, the 2D UI pop-ups shouldn't appear in VR.