www/firefox: update to 60.0
- Add U2F support, required by Web Authentication [1]
- Drop libv4l support to reduce maintenance
Changes: https://www.mozilla.org/firefox/60.0/releasenotes/
PR: 226476
Tested by: tobik, jrm, D. Ebdrup, lwhsu
Submitted by: Greg V [1]
Security: 5aefc41e-d304-4ec8-8c82-824f84f08244
MFH: 2018Q2
Differential Revision: https://reviews.freebsd.org/D15186