Ubuntu 18.04: Firefox showing playback error

I'm facing a strange issue with Firefox Quantum (versions 63.0.x) in my ubuntu 18.04 64 Bit. When i try to open this site http://www.lalegultv.com.tr/canli-yayin which plays video automatically, i'm getting

Your browser doesn't support playback of this video error. 

I tried using this with chrome on ubuntu, it worked perfectly. I also tried with the same browser on my Windows 10 machine. It works perfectly without giving any errors. I don't know why firefox behaves strangely in my ubuntu machine. I have not added any extra plugins or any addons.