Oracle has now certified IE11 (Internet Explorer 11) for WebCenter Portal 184.108.40.206.x and 220.127.116.11.x. You need to implement patch up to 18.104.22.168 with the latest Bundle Patch – kindly refer to Note 1087226.1
Error the end users will see, in IE11 (within a popup):
You are using an unsupported browser. The supported browsers are Internet Explorer 7 and higher, Firefox 22.214.171.124 and higher, Safari 3.1.2 and higher, and Google Chrome 1.0 or higher.
Example of the popup screen:
In summary, there are a number of differences between Microsoft IE 11 and former versions, where one that makes more difference is the change of the User-Agent header string