There are two potential causes, generally.
With modern hardware that supports VP9 codec, try disabling ambient mode. This actually fixed it on my Surface Laptop. Which is not new at all being from 2017 but by video standards is still modern. It supports VP9 and H.265.
https://www.notebookcheck.net/Intel-Cor ... 992.0.html
Here is the info about disabling ambient mode. It's literally like two clicks.
https://www.reddit.com/r/firefox/commen ... o_disable/
For older hardware that does NOT support codecs like VP9 and H.265 or even older hardware that doesn't even support H.264, you can install a browser plug-in that forces H.264 streams. This improves performance on hardware that does support hardware H.264 decode but also for CPU decode like my old Vaio.
Search for a plug-in called h264ify across seemingly any browser. I haven't done research but probably computers 10+ years old are going to fall into needing this, or perhaps newer, lower end ones. Symptoms are high CPU utilization, fan speeds, temps, crappy battery. In my Surface Laptop's case, I was getting these symptoms in Youtube but the issue was ambient mode since as I said it supports hardware VP9 decode.
Fixing Youtube high CPU utilization
Re: Fixing Youtube high CPU utilization
Reddit says 7th gen Intel core, with HD630 or better video (I have the fancier 640 because i7). So my Surface Laptop is the oldest general architecture. More like 8 years old then.kevm14 wrote: Sat Jul 19, 2025 7:54 am With modern hardware that supports VP9 codec, try disabling ambient mode. This actually fixed it on my Surface Laptop. Which is not new at all being from 2017 but by video standards is still modern. It supports VP9 and H.265.
https://www.notebookcheck.net/Intel-Cor ... 992.0.html
I haven't done research but probably computers 10+ years old are going to fall into needing this, or perhaps newer, lower end ones. Symptoms are high CPU utilization, fan speeds, temps, crappy battery. In my Surface Laptop's case, I was getting these symptoms in Youtube but the issue was ambient mode since as I said it supports hardware VP9 decode.