Description of problem:
This happened when trying to use Firefox in a SELinux sandbox by doing sandbox -X firefox. Needless to say, the sandbox didn't start Firefox.
SELinux is preventing /usr/bin/Xephyr from 'connectto' accesses on the unix_stream_socket .

*****  Plugin catchall (100. confidence) suggests   **************************

If you believe that Xephyr should be allowed connectto access on the  unix_stream_socket by default.
Then you should report this as a bug.
You can generate a local policy module to allow this access.
Do
allow this access for now by executing:
# grep Xephyr /var/log/audit/audit.log | audit2allow -M mypol
# semodule -i mypol.pp

Additional Information:
Source Context                unconfined_u:unconfined_r:sandbox_x_t:s0:c135,c756
Target Context                system_u:system_r:xserver_t:s0-s0:c0.c1023
Target Objects                 [ unix_stream_socket ]
Source                        Xephyr
Source Path                   /usr/bin/Xephyr
Port                          <Unknown>
Host                          (removed)
Source RPM Packages           xorg-x11-server-
                              Xephyr-1.15.99.902-7.20140428.fc21.x86_64
Target RPM Packages           
Policy RPM                    selinux-policy-3.13.1-55.fc21.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     (removed)
Platform                      Linux (removed) 3.15.0-0.rc8.git2.2.fc21.x86_64 #1
                              SMP Wed Jun 4 16:32:44 UTC 2014 x86_64 x86_64
Alert Count                   1
First Seen                    2014-06-06 18:30:28 IDT
Last Seen                     2014-06-06 18:30:28 IDT
Local ID                      87b6d38d-fdeb-45ae-9d0c-4b16baabe254

Raw Audit Messages
type=AVC msg=audit(1402068628.466:317): avc:  denied  { connectto } for  pid=13807 comm="Xephyr" path=002F746D702F2E5831312D756E69782F5830 scontext=unconfined_u:unconfined_r:sandbox_x_t:s0:c135,c756 tcontext=system_u:system_r:xserver_t:s0-s0:c0.c1023 tclass=unix_stream_socket


type=SYSCALL msg=audit(1402068628.466:317): arch=x86_64 syscall=connect success=no exit=EACCES a0=0 a1=7fff2be6f500 a2=14 a3=107 items=0 ppid=13798 pid=13807 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000 fsuid=1000 egid=1000 sgid=1000 fsgid=1000 tty=(none) ses=1 comm=Xephyr exe=/usr/bin/Xephyr subj=unconfined_u:unconfined_r:sandbox_x_t:s0:c135,c756 key=(null)

Hash: Xephyr,sandbox_x_t,xserver_t,unix_stream_socket,connectto

Version-Release number of selected component:
selinux-policy-3.13.1-55.fc21.noarch

Additional info:
reporter:       libreport-2.2.2
hashmarkername: setroubleshoot
kernel:         3.15.0-0.rc8.git2.2.fc21.x86_64
type:           libreport