Usually you can't run some Unity games on kongregate or similar websites. To easily solve the problem without headaches on windows 10 you can just install the 4.7.2 version (that works also for 3.x versions) use internet explorer 11 (just run WIN+r "iexplore" ) or a 32 bit 52.3.0 version of firefox (portable). On osx just run safari or an older 52.3.0 version of firefox. Download links for older unity webplayer (as from the unity forums - thank to them) 5.3.x: http://files.unity3d.com/stefan/webplayer/webplayer_archive/ClosedNetworkPlayer_5.3.1f1.zip + http://files.unity3d.com/stefan/webplayer/webplayer_archive/ClosedNetworkPlayer_5.3.2f1.zip + http://files.unity3d.com/stefan/webplayer/webplayer_archive/ClosedNetworkPlayer_5.3.3f1.zip + http://files.unity3d.com/stefan/webplayer/webplayer_archive/ClosedNetworkPlayer_5.3.4f1.zip + http://files.unity3d.com/stefan/webplayer/webplayer_archive/ClosedNetworkPlayer_5.3.5f1.zip + http://files.unity