Unity Web Player Not Working and Solutions Not Working Either!

Hi, I've been doing this course and I have made a web build of a game using Unity 4.7.2f1. However, no matter what unity web built game I try to play, they show me a screen prompting an install of Unity Web Player. I have installed it several times, restarted firefox and still nothing.

I googled up this link and it explains how to do it on google chrome. I'm using Firefox52. I tried enabling NPAPI on firefox but I couldn't figure out how to do it for the unity plugin.

I found this other link which suggested downloading Firefox ESR version. I did and ran it and reinstalled the web player again. Restarted browser. Still nothing. I know I could use UNITY5 and create a WebGL based game instead, but I already have 3 games which are built for the web player and plugin.

Can anyone please help me with this issue? Thanks!