MFH: r454000 r454192
www/firefox: backport FF57+ fixes
No time to track down upstream commits for
https://bugzilla.mozilla.org/buglist.cgi?bug_id=1384615,1386490,1393840,1403716
PR: 222859
Security: f78eac48-c3d1-4666-8de5-63ceea25a578
Approved by: ports-secteam (feld, swills)