Video freezing 4k

Hello,

I have dell inspiron 7559 with 4k screen. 

when i open a 4k movie in youtube with google chrome or firefox the video is stuck or freeze and the audio is not sync to the video. when i open it with microsoft edge or explorer is play smooth.

i  have installed adobe flash bot chrome and firefox but still no changes.

My laptop specs

i7 6700HQ 

8GB

nvidia gtx960m 4 gb ddr5

ssd drive intel

i think the problem is windows 10 but maybe someone have answer for this.

Regards,

Nir