"wheel" event propagates in Firefox

[deltafactory]

Using 2-finger scroll in Windows 10/Firefox 58, both the dropdown list and page scroll. The issue does not exist in Chrome.

I found a Firefox-specific issue which led me to the newer "wheel" event.
https://stackoverflow.com/questions/13274326/firefoxjquery-mousewheel-scroll-event-bug

After adding "wheel.chosen" to the list of events on the following line, the issue was no longer present.
this.search_results.bind('mousewheel.chosen DOMMouseScroll.chosen', function(evt) {

I then was able to observe the situation described in #2823.