This is what I used when I was at the OSL to shut down Firefox on remote systems with a NFS homedir.

netfox.sh

#!/bin/bash
HN=`hostname -f`

echo hostname set to $HN
if test -e ~/.mozilla/firefox/lock_host ; then
    LM=`cat ~/.mozilla/firefox/lock_host`
    echo Firefox has taken a lock out on the following machine:
    cat ~/.mozilla/firefox/lock_host
    if [ "$LM" = "$HN" ] ; then
        echo Running a repeat firefox
        /usr/bin/firefox
        exit
    else
        #kdialog –yesno "Firefox is locked on machine $LM \n Do you wish me to try to kill it?"
        zenity --question --text="Firefox is locked on $LM.\nDo you wish me to try to kill it?"
        if [ $? = 0 ]; then
            echo "Trying to kill the remote firefox"
            ssh -o "StrictHostKeyChecking no" $LM "killall -regexp firefox" 2> /tmp/.netfoxsshres
            RES=`cat /tmp/.netfoxsshres`
            rm -f /tmp/.netfoxsshres
            zenity --info --text="Result was $RES"
        fi
    fi
else
    echo No lock_host detected
    echo Making lock_host
    echo $HN > ~/.mozilla/firefox/lock_host
    echo $(date) Starting on $HN >> ~/.mozilla/firefox/lock_host.log
fi

echo Running firefox
/usr/bin/firefox $@
echo Removing lock_host
rm -f ~/.mozilla/firefox/lock_host
echo $(date) Exiting on $HN >> ~/.mozilla/firefox/lock_host.log