Firefox doesn't autostart in saved session

Binary package hint: xfce4-session

All programs that are openned when I log out (and save session) open when I re-login, except Firefox. Here is my ~/.xsession-errors:
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/etc/gdm/PreSession/Default: Registering your session with wtmp and utmp
/etc/gdm/PreSession/Default: running: /usr/bin/sessreg -a -w /var/log/wtmp -u /var/run/utmp -x "/var/lib/gdm/:0.Xservers" -h "" -l ":0" "alvaro"
/etc/gdm/Xsession: Beginning session setup...

** (xfwm4:5155): WARNING **: The display does not support the XComposite extension.

** (xfwm4:5155): WARNING **: Compositing manager disabled.
env: firefox-bin: Arquivo ou diretório não encontrado
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"Arquivo ou diretório não encontrado" means "File or directory not found"

I think that it occrus because the command to start Mozilla Firefox is 'firefox', don't 'firefox-bin'