Increase browser requirements
- Firefox 60 ESR (released 2018-05-09)
- Chrome 65 (released 2018-03-06)
- Opera 52 (released 2018-03-14)
- Safari 11 (released 2017-09-19)
Support for Firefox ESR 52 was dropped on September 5, 2018. Using
out-of-date browsers should be discouraged as they pose a security risk.