... since JACK audio backend has been implemented since version 50.
A commit references this bug: Author: jbeich Date: Wed Sep 27 04:12:06 UTC 2017 New revision: 450705 URL: https://svnweb.freebsd.org/changeset/ports/450705 Log: gecko: add JACK option (enabled by default) PR: 221464 Changes: head/Mk/bsd.gecko.mk head/mail/thunderbird/Makefile head/mail/thunderbird/files/patch-bug1386957 head/www/firefox/Makefile head/www/firefox/Makefile.options head/www/firefox/files/patch-bug1386957 head/www/firefox/pkg-message head/www/firefox-esr/Makefile head/www/firefox-esr/files/patch-bug1386957 head/www/firefox-esr/pkg-message head/www/libxul/Makefile head/www/seamonkey/Makefile head/www/seamonkey/files/patch-bug1386957