[Firefox] Invoke preventDefault on drop

...such that Firefox does not try to treat drop as a new URL
to navigate to. Addresses #688 and #527

platform/representation/src/gestures/DropGesture.js

@@ -123,6 +123,7 @@ define(
                 // destination domain object's composition, and persist
                 // the change.
                 if (id) {
+                    e.preventDefault();
                     $q.when(action && action.perform()).then(function (result) {
                         //Don't go into edit mode for folders
                         if (domainObjectType!=='folder') {