MFH: r486573 r486574 r486575 r486734 r486823

www/firefox: update to 64.0

Changes: https://www.mozilla.org/firefox/64.0/releasenotes/
PR: 233028
Security: d10b49b2-8d02-49e8-afde-0844626317af
Approved by: ports-secteam (miwi)
Differential Revision: https://reviews.freebsd.org/D17871