Only attempt to use the IE technique for setting opacity if the filter...

Only attempt to use the IE technique for setting opacity if the filter property exists (otherwise fallback to the standards-compatible technique).

src/css.js

@@ -49,7 +49,7 @@ jQuery.extend({
 		var style = elem.style || elem, set = value !== undefined;
 
 		// IE uses filters for opacity
-		if ( !jQuery.support.opacity && name === "opacity" ) {
+		if ( !jQuery.support.opacity && name === "opacity" && style.filter ) {
 			if ( set ) {
 				// IE has trouble with opacity if it does not have layout
 				// Force it by setting the zoom level