User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:81.0) Gecko/20100101 Firefox/81.0

Steps to reproduce:

After the update that fixed https://bugzilla.mozilla.org/show_bug.cgi?id=1645671
my AMD GPU powered desktop has worked great on nightly with both vp9 and h264 decoding, however my IntelHD laptop seems to be having serious issues.

Hardware: i7-8550u, IntelUHD620, 8GB LPDDR3
Software: Mesa - tried both stable and git, happens on both (ubuntu), OS: Pop!_OS 20.04, Kernel 5.8 stable

Actual results:

YouTube: The video starts, first decodes for a few seconds, then automatically switches to (360p) - seems to be related to the codec used, after I switch it back to 1080p it decodes for a few seconds and crashes. Black screen appears with text:
An error occurred. Please try again later. (Playback ID: eHO39SOysMKWKHP-)
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Expected results:

Video decodes and plays normally throughout.

Confirmed, I saw this yesterday in bug 1645672 comment 13. Now we are reliably running into bug 1643855/bug 1645672 and bug 1656436 should fix them.