# yum update selinux-policy-sandbox policycoreutils-sandbox
--enablerepo=updates-testing
selinux-policy-sandbox was not present on my system, I installed it now.
rpm -qa \*sandbox
selinux-policy-sandbox-3.12.1-161.fc20.noarch
policycoreutils-sandbox-2.2.5-4.fc20.x86_64
It still doesn't work:
sandbox -X -t sandbox_web_t firefox
Failed to execute command /usr/share/sandbox/sandboxX.sh: Operation not
permitted
going to downgrade libcap-ng again...