PHP DBG is a great, free debugger for PHP. For more info see: <http://dd.cron.ru/>.
Use of PHP DBG may greatly affect the speed with which the SquirrelMail login page is displayed. After the initial display of the login page, all other pages seem to be displayed quickly.
Turn off PHP DBG if it is not needed. You can do this by editing your php.ini file.
debugger.enabled = false
debugger.JIT_host = clienthost
debugger.JIT_port = 7869