There was an RDD sandboxing bug (bugs?) in the recent Firefox versions that broke VAAPI (hw accelerated video playback).
After months, the RDD bug was finally fixed in Firefox 101, the VAAPI is working now. But, it is unstable, and it causes very long RDD Process coredumps or libc.so.6 segfaults in large numbers. - check your dmesg / journal
If the coredumps or segfaults happening on your system too, then you should again disable the VAAPI by setting this Firefox key to false in about:config, at least until the next Firefox release…