When older IEs throw an error at setting the background-color using RGBA, use something they understand.

dialog-polyfill.js

@@ -189,7 +189,12 @@ var dialogPolyfill = (function() {
     this.overlay.style.position = 'fixed';
     this.overlay.style.left = '0px';
     this.overlay.style.top = '0px';
-    this.overlay.style.backgroundColor = 'rgba(0,0,0,0.0)';
+		try {
+			this.overlay.style.backgroundColor = 'rgba(0,0,0,0.0)';
+		} catch(e) {
+			this.overlay.style.backgroundColor = '#000';
+			this.overlay.style.filter = 'alpha(opacity=0)';
+		}
 
     addEventListenerFn(this.overlay, 'click', function(e) {
       var redirectedEvent = document.createEvent('MouseEvents');