Starting with Firefox 54, on all Firefox channels and platforms, the
Event.prototype.timeStamp property will return a double
DOMHighResTimeStamp value since the page load, consisting of milliseconds in the integer part and microseconds in the decimal part, instead of an integer
DOMTimeStamp value only in milliseconds since the epoch time.
This change has already been made on Firefox Nightly and Developer Edition for Windows, Linux and macOS. As the Android implementation is now complete, the Beta and Release channels also enable high resolution timestamp by default.
Given that Google Chrome has enabled it since Chrome 49 shipped in March 2016, the compatibility risk is considered low at this moment.