Steps to reproduce

1. Browse to any hosted world via Firefox (possibly some other browsers too).

Expected behavior
The scene loads, and interaction can take place.

Actual behavior
The loading bar stops around 5%, or doesn't even show up at all, and the screen behind it remains black.

Additional context
In all cases seen so far, in the console is thrown a TypeError#1: can't access property "value", this.listener.positionX is undefined.