In a0c53a96 SYSTEM_MOZILLA was removed.

Change-Id: I421a293c7611dd5ed0d810c9c8a80f19faf1689a
Reviewed-on: https://gerrit.libreoffice.org/19580Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>