diff --git a/widget/cocoa/nsClipboard.h b/widget/cocoa/nsClipboard.h
index c838f531d098..dfda7130f984 100644
--- a/widget/cocoa/nsClipboard.h
+++ b/widget/cocoa/nsClipboard.h
@@ -32,6 +32,7 @@ class nsClipboard : public nsBaseClipboard {
   // in the parent process. This is needed for the services menu which
   // requires synchronous access to the current selection.
   static mozilla::StaticRefPtr<nsITransferable> sSelectionCache;
+  static int32_t sSelectionCacheChangeCount;
 
   // Helper methods, used also by nsDragService
   static NSDictionary* PasteboardDictFromTransferable(nsITransferable* aTransferable);
@@ -47,6 +48,9 @@ class nsClipboard : public nsBaseClipboard {
                                     int32_t aWhichClipboard) override;
   NS_IMETHOD GetNativeClipboardData(nsITransferable* aTransferable,
                                     int32_t aWhichClipboard) override;
+  mozilla::Result<int32_t, nsresult> GetNativeClipboardSequenceNumber(
+      int32_t aWhichClipboard) override;
+
   void ClearSelectionCache();
   void SetSelectionCache(nsITransferable* aTransferable);
 
diff --git a/widget/cocoa/nsClipboard.mm b/widget/cocoa/nsClipboard.mm
index 0d1c7c688b03..f3183b533086 100644
--- a/widget/cocoa/nsClipboard.mm
+++ b/widget/cocoa/nsClipboard.mm
@@ -29,6 +29,7 @@ using mozilla::gfx::DataSourceSurface;
 using mozilla::gfx::SourceSurface;
 
 mozilla::StaticRefPtr<nsITransferable> nsClipboard::sSelectionCache;
+int32_t nsClipboard::sSelectionCacheChangeCount = 0;
 
 nsClipboard::nsClipboard()
     : nsBaseClipboard(mozilla::dom::ClipboardCapabilities(false /* supportsSelectionClipboard */,
@@ -75,10 +76,11 @@ static NSPasteboard* GetPasteboard(int32_t aWhichClipboard) {
 }  // namespace
 
 void nsClipboard::SetSelectionCache(nsITransferable* aTransferable) {
+  sSelectionCacheChangeCount++;
   sSelectionCache = aTransferable;
 }
 
-void nsClipboard::ClearSelectionCache() { sSelectionCache = nullptr; }
+void nsClipboard::ClearSelectionCache() { SetSelectionCache(nullptr); }
 
 NS_IMETHODIMP
 nsClipboard::SetNativeClipboardData(nsITransferable* aTransferable, nsIClipboardOwner* aOwner,
@@ -774,3 +776,23 @@ nsClipboard::EmptyClipboard(int32_t aWhichClipboard) {
 
   NS_OBJC_END_TRY_BLOCK_RETURN(NS_ERROR_FAILURE);
 }
+
+mozilla::Result<int32_t, nsresult> nsClipboard::GetNativeClipboardSequenceNumber(
+    int32_t aWhichClipboard) {
+  NS_OBJC_BEGIN_TRY_BLOCK_RETURN;
+
+  MOZ_DIAGNOSTIC_ASSERT(nsIClipboard::IsClipboardTypeSupported(aWhichClipboard));
+
+  if (kSelectionCache == aWhichClipboard) {
+    return sSelectionCacheChangeCount;
+  }
+
+  NSPasteboard* cocoaPasteboard = GetPasteboard(aWhichClipboard);
+  if (!cocoaPasteboard) {
+    return mozilla::Err(NS_ERROR_FAILURE);
+  }
+
+  return [cocoaPasteboard changeCount];
+
+  NS_OBJC_END_TRY_BLOCK_RETURN(mozilla::Err(NS_ERROR_FAILURE));
+}
diff --git a/widget/nsBaseClipboard.cpp b/widget/nsBaseClipboard.cpp
index 1af81819ada5..b36b584371c8 100644
--- a/widget/nsBaseClipboard.cpp
+++ b/widget/nsBaseClipboard.cpp
@@ -158,9 +158,11 @@ NS_IMETHODIMP nsBaseClipboard::SetData(nsITransferable* aTransferable,
                                        int32_t aWhichClipboard) {
   NS_ASSERTION(aTransferable, "clipboard given a null transferable");
 
-  CLIPBOARD_LOG("%s", __FUNCTION__);
+  CLIPBOARD_LOG("%s: clipboard=%d", __FUNCTION__, aWhichClipboard);
 
   if (!nsIClipboard::IsClipboardTypeSupported(aWhichClipboard)) {
+    CLIPBOARD_LOG("%s: clipboard %d is not supported.", __FUNCTION__,
+                  aWhichClipboard);
     return NS_ERROR_FAILURE;
   }
 
@@ -178,8 +180,6 @@ NS_IMETHODIMP nsBaseClipboard::SetData(nsITransferable* aTransferable,
   }
   mEmptyingForSetData = false;
 
-  clipboardCache->Update(aTransferable, anOwner);
-
   nsresult rv = NS_ERROR_FAILURE;
   if (aTransferable) {
     mIgnoreEmptyNotification = true;
@@ -189,9 +189,18 @@ NS_IMETHODIMP nsBaseClipboard::SetData(nsITransferable* aTransferable,
   }
   if (NS_FAILED(rv)) {
     CLIPBOARD_LOG("%s: setting native clipboard data failed.", __FUNCTION__);
+    return rv;
   }
 
-  return rv;
+  auto result = GetNativeClipboardSequenceNumber(aWhichClipboard);
+  if (result.isErr()) {
+    CLIPBOARD_LOG("%s: getting native clipboard change count failed.",
+                  __FUNCTION__);
+    return result.unwrapErr();
+  }
+
+  clipboardCache->Update(aTransferable, anOwner, result.unwrap());
+  return NS_OK;
 }
 
 /**
@@ -298,4 +307,5 @@ void nsBaseClipboard::ClipboardCache::Clear() {
     mClipboardOwner = nullptr;
   }
   mTransferable = nullptr;
+  mSequenceNumber = -1;
 }
diff --git a/widget/nsBaseClipboard.h b/widget/nsBaseClipboard.h
index 6d9c064b76fc..a7e2501ca48e 100644
--- a/widget/nsBaseClipboard.h
+++ b/widget/nsBaseClipboard.h
@@ -8,7 +8,7 @@
 
 #include "mozilla/dom/PContent.h"
 #include "mozilla/Logging.h"
-#include "mozilla/UniquePtr.h"
+#include "mozilla/Result.h"
 #include "nsIClipboard.h"
 #include "nsITransferable.h"
 #include "nsCOMPtr.h"
@@ -124,6 +124,8 @@ class nsBaseClipboard : public ClipboardSetDataHelper {
   // Implement the native clipboard behavior.
   NS_IMETHOD GetNativeClipboardData(nsITransferable* aTransferable,
                                     int32_t aWhichClipboard) = 0;
+  virtual mozilla::Result<int32_t, nsresult> GetNativeClipboardSequenceNumber(
+      int32_t aWhichClipboard) = 0;
 
   class ClipboardCache final {
    public:
@@ -138,11 +140,12 @@ class nsBaseClipboard : public ClipboardSetDataHelper {
      */
     void Clear();
     void Update(nsITransferable* aTransferable,
-                nsIClipboardOwner* aClipboardOwner) {
+                nsIClipboardOwner* aClipboardOwner, int32_t aSequenceNumber) {
       // Clear first to notify the old clipboard owner.
       Clear();
       mTransferable = aTransferable;
       mClipboardOwner = aClipboardOwner;
+      mSequenceNumber = aSequenceNumber;
     }
     nsITransferable* GetTransferable() const { return mTransferable; }
     nsIClipboardOwner* GetClipboardOwner() const { return mClipboardOwner; }
@@ -150,6 +153,7 @@ class nsBaseClipboard : public ClipboardSetDataHelper {
    private:
     nsCOMPtr<nsITransferable> mTransferable;
     nsCOMPtr<nsIClipboardOwner> mClipboardOwner;
+    int32_t mSequenceNumber = -1;
   };
 
   mozilla::UniquePtr<ClipboardCache> mCaches[nsIClipboard::kClipboardTypeCount];
diff --git a/widget/windows/nsClipboard.cpp b/widget/windows/nsClipboard.cpp
index f2c16343ee74..e89c2dde4a93 100644
--- a/widget/windows/nsClipboard.cpp
+++ b/widget/windows/nsClipboard.cpp
@@ -1356,6 +1356,12 @@ nsClipboard::EmptyClipboard(int32_t aWhichClipboard) {
   return nsBaseClipboard::EmptyClipboard(aWhichClipboard);
 }
 
+Result<int32_t, nsresult> nsClipboard::GetNativeClipboardSequenceNumber(
+    int32_t aWhichClipboard) {
+  MOZ_DIAGNOSTIC_ASSERT(kGlobalClipboard == aWhichClipboard);
+  return (int32_t)::GetClipboardSequenceNumber();
+}
+
 //-------------------------------------------------------------------------
 NS_IMETHODIMP nsClipboard::HasDataMatchingFlavors(
     const nsTArray<nsCString>& aFlavorList, int32_t aWhichClipboard,
diff --git a/widget/windows/nsClipboard.h b/widget/windows/nsClipboard.h
index 2f0ed4aa3b26..74e87ea2929f 100644
--- a/widget/windows/nsClipboard.h
+++ b/widget/windows/nsClipboard.h
@@ -82,6 +82,8 @@ class nsClipboard : public nsBaseClipboard, public nsIObserver {
                                     int32_t aWhichClipboard) override;
   NS_IMETHOD GetNativeClipboardData(nsITransferable* aTransferable,
                                     int32_t aWhichClipboard) override;
+  mozilla::Result<int32_t, nsresult> GetNativeClipboardSequenceNumber(
+      int32_t aWhichClipboard) override;
 
   static bool IsInternetShortcut(const nsAString& inFileName);
   static bool FindURLFromLocalFile(IDataObject* inDataObject, UINT inIndex,