Smart move on Mozilla's part to start working on VR. The desktop browser space has been saturated for so long, but making a bet on a new space might help them get a toehold on a whole new world.
This doesn't mean they are not focused on desktop, but strategically this is a solid bed that may or may not pay off, but will be key for long-term survival.
EDIT: plus having commercial sponsors for the eventual Servo-in-VR (as noted elsewhere, not shipping yet) will be key to getting Servo itself ready for production.
EDIT 2: Can we get material properties on HTML elements please? I want <img>s with bump-mapping and specular highlights. :)