I am reviving this topic to try and raise attention that the chat still does not work for IE11, despite it being reported ages ago. Please ignore the above nonsense and focus on this critical on-going issue.
Having dredged through a debugger I noticed a rather silly mistake which most certainly is causing most of the problems.
The chat web page is set to IE7 document mode (IE=7.0000) yet the chat.js script uses "EventTarget.addEventListener" which was not supported prior to IE Version 9. The obvious result is that IE11 runs it in IE7 compatibility mode and the script crashes at that point as there is no such function.
Since the script depends heavily on calling that method, backwards compatibility for IE7 has been trashed anyway. Also since XP is no longer supported and versions below IE11 are mostly found on XP systems one might as well drop full support for IE7 and raise it straight to IE11 (people using XP will just have to use Fire Fox, Chrome or another browser which supports it). One could even go as far as targeting the latest IE version with "IE=Edge" however that is not too recommended as you cannot guarantee that all methods will keep being supported.
After changing the document mode support to IE11 on a local copy the chat loaded considerably further. The only thing that stopped it from working then was some "access denied" open error which is probably because I was running the script locally and not from the web site meaning that the environment was different.
To recap the above. Ralle (or whoever maintains the chat code), you need to raise the IE document mode on the chat web page from 7 to at least 9 (newer is probably better with 11 or Edge being the lattest).