The cuas is that libcanberra is missing. This should be in the dependencies.
A commit references this bug: Author: jbeich Date: Sun Mar 8 18:10:53 UTC 2015 New revision: 380782 URL: https://svnweb.freebsd.org/changeset/ports/380782 Log: - Add CANBERRA and enable by default for Thunderbird and SeaMonkey [1] - Bump version requirements for harfbuzz and libvorbis PR: 198142 [1] See also: https://dxr.mozilla.org/comm-central/search?q=nsISound [1] Changes: head/Mk/bsd.gecko.mk head/mail/thunderbird/Makefile head/mail/thunderbird/files/patch-z-bug517422 head/www/firefox/Makefile head/www/firefox/Makefile.options head/www/firefox/files/patch-bug847568 head/www/firefox/files/patch-z-bug517422 head/www/firefox-esr/Makefile head/www/firefox-esr/files/patch-z-bug517422 head/www/libxul/Makefile head/www/libxul/files/patch-z-bug517422 head/www/seamonkey/Makefile head/www/seamonkey/files/patch-bug847568 head/www/seamonkey/files/patch-z-bug517422
Thanks. Added as an optional dependency. Note, as sound themes aren't pulled by audio/libcanberra, only beep() and play(URL) always work. playEventSound(event) uses the algorithm described in the following link, e.g. for message-new-email. Picking a sound theme is outside of scope for gecko@. http://0pointer.de/public/sound-theme-spec.html#sound_lookup