Unmask www-client/firefox-32.0

Because www-client/firefox-29.0.1 is gone.
Unmask app-emulation/virtualbox-4.3.16

Because app-emulation/virtualbox-4.3.12 is gone.
www-client/firefox: use system-wide cairo, icu, jpeg and sqlite
Prefer dev-db/mariadb over dev-db/mysql