I tested https://jsfiddle.net/x2r3jpuz/2/ on IE11, and it is not causing a crash for me. This is the version info for my IE11:

If Microsoft has apparently fixed whatever bug was causing that problem, should the code switch back to using MutationObservers instead of MutationEvents, since MDN's docs say MutationEvents are deprecated and can make DOM modifications "1.5 - 7 times slower?"