Why MASTER_SITE_MOZILLA + contrib in seamonkey-bin/Makefile.common?

[OBATA Akio <obache%NetBSD.org@localhost>]

Anyone know why followings is required in www/seamonkey-bin/Makefile.common?
Why need to add "contrib/"?

Anyway, it does not work as expected.
MASTER_SITE_MOZILLA is not defined here unless defined in /etc/mk.conf.
So, MASTER_SITES result in empty (ex. www/firefox-bin).

.if !defined(MASTER_SITES)
_MASTER_SITES+= 
${MASTER_SITE_MOZILLA:=${MOZILLA_SHORT}/releases/${MOZ_DIR}/}
.  for _site_ in ${_MASTER_SITES}
MASTER_SITES+=          ${_site_}
MASTER_SITES+=          ${_site_}contrib/
.  endfor
.endif

--
"Of course I love NetBSD":-)
OBATA Akio / obache%NetBSD.org@localhost