[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/features/timeline/src/directives/MCTSwimlaneDrop.js

@@ -91,6 +91,7 @@ define(
 
                 if (id) {
                     event.stopPropagation();
+                    e.preventDefault();
                     // Delegate the drop to the swimlane itself
                     swimlane.drop(id, droppedObject);
                 }

platform/features/timeline/test/directives/MCTSwimlaneDropSpec.js

@@ -162,6 +162,11 @@ define(
                 expect(mockScope.$apply).toHaveBeenCalled();
             });
 
+            it("invokes preventDefault on drop", function () {
+                handlers.drop(testEvent);
+                expect(testEvent.preventDefault).toHaveBeenCalled();
+            });
+
             it("clears highlights when drag leaves", function () {
                 mockSwimlane.highlight.andReturn(true);
                 handlers.dragleave();