--- a/mobile/android/components/geckoview/GeckoViewExternalAppService.js
+++ b/mobile/android/components/geckoview/GeckoViewExternalAppService.js
@@ -18,22 +18,20 @@ function ExternalAppService() {
 }
 
 ExternalAppService.prototype = {
   classID: Components.ID("{a89eeec6-6608-42ee-a4f8-04d425992f45}"),
   QueryInterface: ChromeUtils.generateQI([Ci.nsIExternalHelperAppService]),
 
   doContent(mimeType, request, context, forceSave) {
     const channel = request.QueryInterface(Ci.nsIChannel);
-    const mm = context.QueryInterface(Ci.nsIDocShell).tabChild.messageManager;
-
     debug `doContent: uri=${channel.URI.displaySpec}
                       contentType=${channel.contentType}`;
 
-    EventDispatcher.forMessageManager(mm).sendRequest({
+    GeckoViewUtils.getDispatcherForWindow(context).sendRequest({
       type: "GeckoView:ExternalResponse",
       uri: channel.URI.displaySpec,
       contentType: channel.contentType,
       contentLength: channel.contentLength,
       filename: channel.contentDispositionFilename
     });
 
     request.cancel(Cr.NS_ERROR_ABORT);