--- a/mobile/android/components/geckoview/GeckoViewPrompt.js
+++ b/mobile/android/components/geckoview/GeckoViewPrompt.js
@@ -364,17 +364,17 @@ function PromptDelegate(aDomWin) {
   if (!aDomWin) {
     return;
   }
   let gvWin = aDomWin.QueryInterface(Ci.nsIInterfaceRequestor)
                      .getInterface(Ci.nsIDocShell).QueryInterface(Ci.nsIDocShellTreeItem)
                      .rootTreeItem.QueryInterface(Ci.nsIInterfaceRequestor)
                      .getInterface(Ci.nsIDOMWindow);
   try {
-    this._dispatcher = EventDispatcher.for(gvWin);
+    this._dispatcher = gvWin.WindowEventDispatcher || EventDispatcher.for(gvWin);
   } catch (e) {
     // Use global dispatcher.
   }
 }
 
 PromptDelegate.prototype = {
   QueryInterface: XPCOMUtils.generateQI([Ci.nsIPrompt]),