8K video is extremely taxing on your system and your network. In addition to having a great PC, you also need lightning quick internet. Google has said that you need a consistent download speed of at least 50Mbps.

When 8K video was first released back in 2015, Firefox didn't even support the format. It's been a few years now, so I'm sure that's changed, but I can't say for sure.

You can try typing about:config in the Firefox address bar and changing the media.mediasource.webm.enabled preference to true to see if it improves the situation at all.

I have 1000Mbps internet and I tried what you suggested, the videos don't freeze anymore but it stutters.

1kbps isn't the speed you will get on a 24/7 constant basis that is the ISP advertised speed range you get. Your ISP is no guarantee 8k video is problem free. So let's not confuse ISP rated speed with your actual internet speed. And also as mentioned 8K streaming is taxing regardless of your hardware specs they are streaming to your PC not directly form your PC.

WestEnd said

1kbps isn't the speed you will get on a 24/7 constant basis that is the ISP advertised speed range you get. Your ISP is no guarantee 8k video is problem free. So let's not confuse ISP rated speed with your actual internet speed. And also as mentioned 8K streaming is taxing regardless of your hardware specs they are streaming to your PC not directly form your PC.

I understand , but I will mention that about 4 months ago I was able to play 8k videos on Firefox without any stutters or freezing and I had the same hardware, internet.

You have to also consider ISP throttle as well which you left out. Also time of the day can also make difference in speeds.

Well I tried downloading other browsers like google chrome and Microsoft edge to test and they seem to run the 8k videos fine.

What's the link then?

https://youtu.be/1La4QzGeaaQ