www/firefox: backport more 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
MFH: 2017Q4 (r454000 followup, FF57 alternative until 2018Q1)