OrbitControls: Added Firefox support. Fixes #2908.

examples/js/controls/OrbitControls.js

@@ -275,7 +275,19 @@ THREE.OrbitControls = function ( object, domElement ) {
 
 		if ( ! scope.userZoom ) return;
 
-		if ( event.wheelDelta > 0 ) {
+		var delta = 0;
+
+		if ( event.wheelDelta ) { // WebKit / Opera / Explorer 9
+
+			delta = event.wheelDelta;
+
+		} else if ( event.detail ) { // Firefox
+
+			delta = - event.detail;
+
+		}
+
+		if ( delta > 0 ) {
 
 			scope.zoomOut();
 
@@ -290,5 +302,6 @@ THREE.OrbitControls = function ( object, domElement ) {
 	this.domElement.addEventListener( 'contextmenu', function ( event ) { event.preventDefault(); }, false );
 	this.domElement.addEventListener( 'mousedown', onMouseDown, false );
 	this.domElement.addEventListener( 'mousewheel', onMouseWheel, false );
+	this.domElement.addEventListener( 'DOMMouseScroll', onMouseWheel, false ); // firefox
 
 };