Since this thread was started Chrome based web browsers have disabled the NPAPI. The Unity Web Player uses the NPAPI and they have yet to release a modern version of their plugin. NPAPI is 20 years old and terrible. Its been replaced with the PPAPI. Only one major browser still supports it: Firefox. Firefox will be dropping it at the end of the year. IE still supports it but since its development has basically ended in favor of edge we wont count it.
