Flash Player 9 causes an illegal instruction when watching videos. This happens
after some (seemingly random) time of watching (1-2 minutes). Everything works
normally otherwise.
This is similar to segfaults reported on this forum (probably not related
though).
I use it with firefox 1.5.0.8 in Ubuntu.
Version 7 used to work flawlessly.

I'm having this same problem, though I'm using Firefox 2.0.0.1. It happens
mostly on Youtube, the video will play for a random amount of time, then it
will stop and Firefox will be frozen. I have the illegal instruction error
occur randomly on other sites using Flash as well, though most of the time
other sites are ok. Flash 7 works fine on Youtube, but most other sites now
require at least version 8, so it doesn't really help me. I'm also on an
Athlon XP processor, and I've tried reinstalling just about all software
involved.

On a side note, why doesn't the uninstaller for Flash work properly? It fails
to close the browser windows itself, so the kill_browser process has to be
ended manually in the task manager, and after completion, the uninstaller
process remains an active process for no reason (this happens with the
installer as well).