MFH: r495403 r495404 r495671 r495681 r495814

www/firefox: update to 66.0

Changes: https://www.mozilla.org/firefox/66.0/releasenotes/
PR: 235300
Security: 05da6b56-3e66-4306-9ea3-89fafe939726
Approved by: ports-secteam (joneum)
Differential Revision: https://reviews.freebsd.org/D19020