While some of us had it turned on for some time, some didn't. Looks like it is fully stable now.
Yey! Test it by starting intel_gpu_top
and than playing video in firefox, if row "Video" goes over 0.0% it is working!
intel-gpu-top: Intel Coffeelake (Gen9) @ /dev/dri/card0 - 921/ 925 MHz; 38% RC6
1.78/10.41 W; 813 irqs/s
IMC reads: 3883 MiB/s
IMC writes: 1632 MiB/s
ENGINES BUSY MI_SEMA MI_WAIT
Render/3D 12.82% |████▊ | 0% 0%
Blitter 0.00% | | 0% 0%
Video 27.99% |██████████▍ | 0% 0%
VideoEnhance 0.00% | | 0% 0%
PID NAME Render/3D Blitter Video VideoEnhance
578 RDD Process | || ||███ || |
32431 firefox-bin |▊ || || || |
2301 elogind-daemon |▌ || || || |
4151 pcmanfm-qt | || || || |
4153 keepassxc | || || || |
4154 pasystray | || || || |
4521 slack | || || || |
6067 chrome | || || || |
29222 jcef_helper | || || || |
Of course, you need second monitor, it goes down to 0 if video is not visible, since Firefox is not rendering it.
Official release notes: https://www.mozilla.org/en-US/firefox/115.0/releasenotes/
Even better when we remind ourselves that GTK means "Gimp ToolKit" :)