Fox and Chrome both can do 4k. I guess I'm more interested in Fox, since its latest iteration is pretty darn impressive and lighter on resources than Chrome. Offtopic: - can you watch Netflix in 4k on a MacOS these days? MS has struck some money-making deal with Netflix where only they can decode DRMed 4k in MS Edge Browser. It really worked when I tested it.
With Firefox 63, 71 degrees Fahrenheit ambient temp, screen full brightness, ublock origin installed, MBP on a wood table. 4K 60 FPS.
The Mac CPU holds 76 Celsius and does a good job of it. With that temp the fans stabilize at 3400 and 3600 RPM. If the cpu temp goes higher for any reason (video loading or interacting with the OS), the fans spin up to around 4400 and 4600 RPM and bring the CPU temp back down to 76 no problem. Once the video is paused the temps come down immediately. I admit the ambient air is on the cool side, so with any adverse conditions I can see the temps being 10-15 degrees higher or higher fan speed.
CPU cores running at 25%-30% the entire time.
GPU cores running between 50%-66% entire time.
Memory not even sweating at a solid 14% usage. (16gb config)
I agree its quite frustrating that safari doesn't support 4k, along with their other products..
The playback on Firefox looked amazing.
No 4k playback in Netflix with any browser in macOS. That I know of..