Alright, created a profile and followed the guide but no luck.
Went to about:profiles > Create new profile > Entered name > Finish
Then for that new profile I clicked on Launch profile in new browser
ubuntu-restricted-extras is already installed as before.
Here are my changes to about:config
media.ffmpeg.vaapi.enabled : true (was false)
media.ffvpx.enabled : false (was true)
media.rdd-vpx.enabled: false (was true)
media.navigator.mediadatadecoder_vpx_enabled : true (was false)
gfx.webrender.all : true (was false)
about:support -
MOZ_LOG
$ MOZ_LOG="PlatformDecoderModule:5" firefox
[Child 13875: Main Thread]: D/PlatformDecoderModule PDMInitializer, Init PDMs in Content process
[Child 13875: Main Thread]: D/PlatformDecoderModule VA-API FFmpeg is disabled by platform
[Child 13875: Main Thread]: D/PlatformDecoderModule VA-API FFmpeg is disabled by platform
Gdk-Message: 18:36:01.668: Unable to load split_v from the cursor theme
[Child 13983: Main Thread]: D/PlatformDecoderModule PDMInitializer, Init PDMs in Content process
[Child 13983: Main Thread]: D/PlatformDecoderModule VA-API FFmpeg is disabled by platform
[Child 13983: Main Thread]: D/PlatformDecoderModule VA-API FFmpeg is disabled by platform
[Child 13983: Main Thread]: D/PlatformDecoderModule Agnostic decoder supports requested type
intel-gpu-top - 127/ 126 MHz; 77% RC6; 0.43 Watts; 158 irqs/s
IMC reads: 2743 MiB/s
IMC writes: 1089 MiB/s
ENGINE BUSY MI_SEMA MI_WAIT
Render/3D/0 18.10% |██████▎ | 0% 0%
Blitter/0 0.00% | | 0% 0%
Video/0 0.00% | | 0% 0%
VideoEnhance/0 0.00% | | 0% 0%