MFH: r501604 r501832

www/firefox: update to 67.0

Changes: https://www.mozilla.org/firefox/67.0/releasenotes/
PR: 236651
Security: 44b6dfbf-4ef7-4d52-ad52-2b1b05d81272
Approved by: ports-secteam (miwi)
Differential Revision: https://reviews.freebsd.org/D19654