Just finished reinstalling 20.04 +update. Firefox is still freezing. Chromium works. Maybe Mozzila "nailed" this to all ubuntu versions. It says version 99.0
if I run it from terminal:
$ firefox
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
[2022-04-24T20:25:53Z ERROR mp4parse] Found 2 nul bytes in "\u{0}\u{0}"
[2022-04-24T20:25:53Z ERROR mp4parse] Found 2 nul bytes in "\u{0}\u{0}"
[2022-04-24T20:25:53Z ERROR mp4parse] Found 2 nul bytes in "\u{0}\u{0}"
[2022-04-24T20:25:53Z ERROR mp4parse] Found 2 nul bytes in "\u{0}\u{0}"
Edit. Same happens on the other laptop. firefox 99.0.1. So only on a HP Z400 Ubuntu 22.04 is usable for me until now.