diff --git a/widget/cocoa/MOZMenuOpeningCoordinator.h b/widget/cocoa/MOZMenuOpeningCoordinator.h
index 3e4dfe61f09d..43a366f24b52 100644
--- a/widget/cocoa/MOZMenuOpeningCoordinator.h
+++ b/widget/cocoa/MOZMenuOpeningCoordinator.h
@@ -8,6 +8,12 @@
 
 #import <Cocoa/Cocoa.h>
 
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+class Runnable;
+}
+
 /*
  * MOZMenuOpeningCoordinator is a workaround for the fact that opening an NSMenu creates a nested
  * event loop. This event loop is only exited after the menu is closed. The caller of
@@ -32,6 +38,10 @@
 // Can only be called on the main thread.
 - (void)cancelAsynchronousOpening:(NSInteger)aHandle;
 
+// Run aRunnable once the nested event loop of the currently open menu has been exited.
+// If no menu is currently open, post the runnable with NS_DispatchToCurrentThread.
+- (void)runAfterMenuClosed:(RefPtr<mozilla::Runnable>&&)aRunnable;
+
 @end
 
 #endif  // MOZMenuOpeningCoordinator_h
diff --git a/widget/cocoa/MOZMenuOpeningCoordinator.mm b/widget/cocoa/MOZMenuOpeningCoordinator.mm
index a482aa5a9e30..8b60431e17f9 100644
--- a/widget/cocoa/MOZMenuOpeningCoordinator.mm
+++ b/widget/cocoa/MOZMenuOpeningCoordinator.mm
@@ -14,7 +14,9 @@
 
 #include "nsCocoaFeatures.h"
 #include "nsCocoaUtils.h"
+#include "nsDeque.h"
 #include "nsObjCExceptions.h"
+#include "nsThreadUtils.h"
 #include "SDKDeclarations.h"
 
 @interface MOZMenuOpeningInfo : NSObject
@@ -32,6 +34,10 @@
   // time at at which it is unqueued in _runMenu.
   MOZMenuOpeningInfo* mPendingOpening;  // strong
 
+  // Any runnables we want to run after the current menu event loop has been exited.
+  // Only non-empty if mRunMenuIsOnTheStack is true.
+  nsRefPtrDeque<mozilla::Runnable> mPendingAfterMenuCloseRunnables;
+
   // An incrementing counter
   NSInteger mLastHandle;
 
@@ -99,6 +105,12 @@
     }
 
     [info release];
+
+    // We have exited _openMenu's nested event loop. Dispatch any pending "after menu close"
+    // runnables to the event loop.
+    while (mPendingAfterMenuCloseRunnables.GetSize() != 0) {
+      NS_DispatchToCurrentThread(mPendingAfterMenuCloseRunnables.PopFront());
+    }
   }
 
   mRunMenuIsOnTheStack = NO;
@@ -111,6 +123,16 @@
   }
 }
 
+- (void)runAfterMenuClosed:(RefPtr<mozilla::Runnable>&&)aRunnable {
+  MOZ_RELEASE_ASSERT(aRunnable);
+
+  if (mRunMenuIsOnTheStack) {
+    mPendingAfterMenuCloseRunnables.Push(aRunnable.forget());
+  } else {
+    NS_DispatchToCurrentThread(aRunnable.forget());
+  }
+}
+
 - (void)_openMenu:(NSMenu*)aMenu atScreenPosition:(NSPoint)aPosition forView:(NSView*)aView {
   // There are multiple ways to display an NSMenu as a context menu.
   //