Bug 218415 - Firefox 63 supports Window.event (#2757)
Bug 218415 - Firefox 63 supports Window.event (#2757)

This is now supported in Firefox. Also, it is no longer
non-standard.
mdn/browser-compat-data,teoli2003/browser-compat-data,chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data