MFH: r428102 r428261
www/firefox: update to 50.1.0
Changes: https://www.mozilla.org/firefox/50.1.0/releasenotes/
Changes: https://hg.mozilla.org/releases/mozilla-release/shortlog
Security: 512c0ffd-cd39-4da4-b2dc-81ff4ba8e238
Approved by: ports-secteam (junovitch)