As you may know, Mozilla Firefox recently removed their support of Unity Web Player. However, I have found an alterantive browser which is still supporting Unity. Palemoon is a browser developed and released by Mozilla, the same company which runned Firefox. Although, I do not stand for that Palemoon is completely safe to use. It is YOUR choice to use it and you should be careful about what information you give out, as always when browsing on the internet.
Palemoon can be downloaded here:
https://www.palemoon.org/palemoon-win32.shtml