cross-browser compatibility for use mouse event "target"

[therewasaguy]

Mouse events are using e.toElement and e.srcElement, but we're getting e.toElement is undefined in Firefox, where mouse event properties like toElement, fromElement, and srcElement aren't implemented.

I think we can use e.target for all of these. And there might be places where e.currentTarget, and e.relatedTarget will come in handy. These three are compatible across browsers.

More info:
http://stackoverflow.com/questions/31865416/what-is-the-difference-between-event-target-event-toelement-and-event-srcelemen

https://developer.mozilla.org/en-US/docs/Web/API/Event/Comparison_of_Event_Targets