freebsd/bugzilla is a set of changes and extensions for Bugzilla being used by the FreeBSD project. Those usually map a Bugzilla source package layout in a 1:1 fashion.
freebsd/bugzilla will refer to a certain bugzilla package from the FreeBSD ports, usually the latest stable one (devel/bugzilla44 as of now).
Thus, if you install devel/bugzilla44, you can simply copy freebsd/bugzilla over ${PREFIX}/www/bugzilla to have a Bugzilla implementation that resembles what the FreeBSD project uses at https://bugs.freebsd.org/bugzilla.
In short:
- cd /usr/ports/devel/bugzilla44 && make install clean
- Download the latest stable freebsd/bugzilla release from https://github.com/freebsd/bugzilla
- tar -C /usr/local/www/bugzilla -xjvf freebsd-bugzilla-ext.tar.bz2
- cd /usr/local/www/bugzilla && checksetup.pl