wget http://dm-download02.mozilla.org/pub/mozilla.org/firefox/releases/11.0/linux-i686/it/firefox-11.0.tar.bz2
tar xvjf firefox-11.0.tar.bz2
sudo mv firefox /opt/firefox
sudo mv /usr/bin/firefox /usr/bin/firefox-old
sudo ln -s /opt/firefox/firefox /usr/bin/firefox
sudo rm firefox-11.0.tar.bz2
killall firefox