Trouble playing the game via MacBook

I am not quit sure this is the place to put this, but I found no accurately corresponding topic for this.

I have a player that tried to play my small game via his macbook.
The problem being, I only made a windows deployement and web deployement.

I figured Mac and Linux users would be able to play through web, as has been the case so far, but it seems one player can't get the game to start (He tried Chrome, Safari and Firefox).

He is trying to play on a MacBook Pro OSX El Capitan 10.11.6 and when going on the corresponding page, the game does not launch at all. I had other Mac and linux users confirming it worked just fine on chrome and firefox so I don't understand what could be going wrong.

Would there be someone kind enough to help me out ? Or maybe point to some data/information that can help me figure it out ?

Thanks for any reply. :)