--- a/testing/mochitest/tests/SimpleTest/EventUtils.js
+++ b/testing/mochitest/tests/SimpleTest/EventUtils.js
@@ -206,16 +206,20 @@ function sendDragEvent(aEvent, aTarget, 
   var relatedTargetArg = aEvent.relatedTarget || null;
   var dataTransfer     = aEvent.dataTransfer  || null;
 
   event.initDragEvent(typeArg, canBubbleArg, cancelableArg, viewArg, detailArg,
                       screenXArg, screenYArg, clientXArg, clientYArg,
                       ctrlKeyArg, altKeyArg, shiftKeyArg, metaKeyArg,
                       buttonArg, relatedTargetArg, dataTransfer);
 
+  if (aEvent._domDispatchOnly) {
+    return aTarget.dispatchEvent(event);
+  }
+
   var utils = _getDOMWindowUtils(aWindow);
   return utils.dispatchDOMEventViaPresShell(aTarget, event, true);
 }
 
 /**
  * Send the char aChar to the focused element.  This method handles casing of
  * chars (sends the right charcode, and sends a shift key for uppercase chars).
  * No other modifiers are handled at this point.
@@ -2129,16 +2133,17 @@ function createDragEventObject(aType, aD
   // nsContentUtils::SetDataTransferInEvent for actual impl).
   dataTransfer.dropEffect = aDataTransfer.dropEffect;
 
   return Object.assign({
     type: aType,
     screenX: destScreenX, screenY: destScreenY,
     clientX: destClientX, clientY: destClientY,
     dataTransfer: dataTransfer,
+    _domDispatchOnly: aDragEvent._domDispatchOnly,
   }, aDragEvent);
 }
 
 /**
  * Emulate a event sequence of dragstart, dragenter, and dragover.
  *
  * @param aSrcElement   The element to use to start the drag.
  * @param aDestElement  The element to fire the dragover, dragenter events