User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20171112125346 Steps to reproduce: Visited a website with a large select (1200+ option tags) that hides and disables options based on search. There appears to be a script that runs inefficiently on disabled options when you click to open the select. There are no https://jsfiddle.net/fnztu9ua/ Compare with the same select sans disabled options: https://jsfiddle.net/q634njfe/ Actual results: It takes a noticeably longer time to open a select with many disabled options. Expected results: There should be no great difference between opening a select with many disabled options, and one with no disabled options.

Tommy, does your proto fix this issue as well?

I think this issue is as same as Bug 1118086. There are also lots of options in the dropdown menu, and it spends too much time on IPC. I tried it on my patch that I worked for Bug 1421229. This case works well without any performance issue.