Use Cesium 19372e2b83 to fix FireFox18 not displaying Earth.

Bug introduced in FireFox 18, worked around by Cesium:
https://github.com/AnalyticalGraphicsInc/cesium/commit/610507dacc9b2bc282729baab5835efd6713232e

Tested on FF 18, FF 19, FF 20 (aurora)

Make sure you do Tools -> Clear Recent History -> Cache: 1 day (or more)
Doing simple Tools -> Clear Cache did NOT work for me.