This question was asked and answered in 2011. However, the web scene has taken a considerable change and now IE6 and IE7 are out, IE8-10 are barely out (under 1% each) and only IE11 is still there.
So, in 2016, do you need to manually remove event listeners to avoid memory leaks? Consider only IE11 for the answer please. I am asking because I created a small library as an alternative to jQuery and would love to know if I have to remove them manually first. Of course the question is when using vanilla javascript, not jQuery.