Just tested a little more, and my game is running well over 3600 ticks/sec in IE11. I'm running it on a newly installed Win 7 64 bit Ultimate OS. IE11 is updated and so is Win 7 (no weird addons or similar stuff). Graphics card is an old ATI HD4600 with newest driver. It has caused me zero problems for the past 4 years.
I will look more into it later today.
On a sidenote, what a great performance gain I experienced switching from old Win XP x64 Pro to Win 7 (in all browsers).