It looks like you might not be building Firefox directly from www/firefox since you're getting the FreeBSD GNOME team messages after it fails. It usually is a matter of updating your sources through cvsup, rebuilding everything with portupgrade, and trying again. This is basically what you would do:
Code:
# cp /usr/share/examples/cvsup/ports-supfile /root/ports-supfile
Edit ports-supfile to grab the sources from a nearby cvsup server.
Code:
# cvsup -g -L 2 /root/ports-supfile
# portupgrade -aRr
# cd /usr/ports/www/firefox
# make install clean