What might make "Xclients" be executed twice when boot system?

For some special purpose, I modified /etc/X11/xinit/Xclients to start firefox instead of start Desktop Environment.

# Argh! Nothing good is installed. Fall back to twm
{
    # gosh, neither fvwm95 nor fvwm2 is available;
    # fall back to failsafe settings
    [ -x /usr/bin/xsetroot ] && /usr/bin/xsetroot -solid '#222E45'

#    if [ -x /usr/bin/xclock ] ; then
#       /usr/bin/xclock -geometry 100x100-5+5 &
#    elif [ -x /usr/bin/xclock ] ; then
#       /usr/bin/xclock -geometry 100x100-5+5 &
#    fi
#    if [ -x /usr/bin/xterm ] ; then
#        /usr/bin/xterm -geometry 80x50-50+150 &
#    fi
    if [ -x /usr/bin/firefox ]; then
     /usr/bin/firefox -chrome http://127.0.0.1/ -width 1280 -height 768
    fi
#    if [ -x /usr/bin/twm ] ; then
#       exec /usr/bin/twm
#    fi

This used to work fine until today I tested it on another computer. Firefox reports that there's another running instanc开发者_高级运维e of firefox which stops responding. Thus, firefox could not autostart as I expected.

I connected the computer with SSH and I found there are 2 firefox processes:

[root@my113 xinit]# ps -ef | grep firefox
root      4479  4371  0 17:34 ?        00:00:00 /bin/sh /usr/lib/firefox-3.0b5/run-mozilla.sh /usr/lib/firefox-3.0b5/firefox -chrome http://127.0.0.1/ -width 1280 -height 768
root      4600  4479  0 17:34 ?        00:00:01 /usr/lib/firefox-3.0b5/firefox -chrome http://127.0.0.1/ -width 1280 -height 768
root      4940  4906  0 17:35 ?        00:00:00 /bin/sh /usr/lib/firefox-3.0b5/run-mozilla.sh /usr/lib/firefox-3.0b5/firefox -chrome http://127.0.0.1/ -width 1280 -height 768
root      4963  4940  0 17:35 ?        00:00:00 /usr/lib/firefox-3.0b5/firefox -chrome http://127.0.0.1/ -width 1280 -height 768
root      5717  5345  0 17:51 pts/2    00:00:00 grep firefox

I guess, for some reason, "Xclients" is executed twice. But I really knows very little about XWindows, so if anyone here could give me some clues, I will appreciate!

Check also the .xsession and .xinitrc files that are found in your home directory. Maybe they contain firefox there as well?