URL field not clickable in Read-Only mode?

This is the typical behavior in 2011 - not just UR12.

You can make the field clickable with some JavaScript:

function OnLoad() {
    //Readonly form
    if (Xrm.Page.ui.getFormType() == 4) {
        //Enable field
        Xrm.Page.ui.controls.get("websiteurl").setDisabled(false);
        //Even though for is read only - this removes the pop up asking you save 
        //when closing the record if the field changed
        Xrm.Page.getAttribute("websiteurl").setSubmitMode("never");
    }
}