http://www.ghacks.net/2016/04/11/fir...-end-of-npapi/

Those of you who are using Unity to run this game should know that Firefox is planning to drop support for Unity (along with all other NPAPI plugins other than Flash) this April. There are two options for you once this happens:

1) Go back to playing this game with its WebGL client.

2) Switch from Firefox to Pale Moon, which will still be compatible with Unity.