Do you by chance have beagled running? Although I have not experienced
it, I have seen messages that beagle can cause similar conditions.
No I don't.
It is not gnome, but rather something else that triggers this behavior
under certain conditions as you yourself said above. It is
intermittent, sometimes fast and other times dog slow.
I have seen, that there are dozens of language extensions installed in
firefox. I have sometimes tried some extensions, that slowed down
firefox very much. But usually this could be solved by uninstalling or
deactivating the extension. It also was firefox that consumed more CPU
then. In this case it's the X-Server and not firefox, that needs the
more CPU time.
