cd /opt/
tar xf "${firefox_filename}"
rm "${firefox_filename}"
-ln -s /opt/firefox/firefox /usr/local/bin/
+ln -f -s /opt/firefox/firefox /usr/local/bin/
update-alternatives --install /usr/bin/x-www-browser x-www-browser /opt/firefox/firefox 200
update-alternatives --set x-www-browser /opt/firefox/firefox