"SELinux runs a Firefox in a restricted session that doesn't have access
to rest of the system. That includes the X session. Firefox will run in
a nested X server (Xephyr), and you won't be able to even copy & paste
from or to the Firefox session and other apps. /But/, it also means that
Firefox is totally restricted from reading any other files on your
system and that malicious Web pages or attacks on plugins like Flash are
sandboxed as well."