diff --git a/dom/base/nsContentAreaDragDrop.cpp b/dom/base/nsContentAreaDragDrop.cpp
index 722064e34e9a..7f5bbe84f794 100644
--- a/dom/base/nsContentAreaDragDrop.cpp
+++ b/dom/base/nsContentAreaDragDrop.cpp
@@ -230,12 +230,10 @@ CheckAndGetExtensionForMime(const nsCString& aExtension,
 NS_IMETHODIMP
 nsContentAreaDragDropDataProvider::GetFlavorData(nsITransferable *aTransferable,
                                                  const char *aFlavor,
-                                                 nsISupports **aData,
-                                                 uint32_t *aDataLen)
+                                                 nsISupports **aData)
 {
-  NS_ENSURE_ARG_POINTER(aData && aDataLen);
+  NS_ENSURE_ARG_POINTER(aData);
   *aData = nullptr;
-  *aDataLen = 0;
 
   nsresult rv = NS_ERROR_NOT_IMPLEMENTED;
 
@@ -345,7 +343,6 @@ nsContentAreaDragDropDataProvider::GetFlavorData(nsITransferable *aTransferable,
     // send back an nsIFile
     if (NS_SUCCEEDED(rv)) {
       CallQueryInterface(file, aData);
-      *aDataLen = sizeof(nsIFile*);
     }
   }
 
diff --git a/widget/nsITransferable.idl b/widget/nsITransferable.idl
index 14fc96a37b58..f7521ac4b7aa 100644
--- a/widget/nsITransferable.idl
+++ b/widget/nsITransferable.idl
@@ -86,9 +86,8 @@ interface nsIFlavorDataProvider : nsISupports
     * @param  aTransferable (in parameter) the transferable we're being called for.
     * @param  aFlavor (in parameter) the flavor of data to retrieve
     * @param  aData the data. Some variant of class in nsISupportsPrimitives.idl
-    * @param  aDataLen the length of the data
     */
-  void getFlavorData(in nsITransferable aTransferable, in string aFlavor, out nsISupports aData, out unsigned long aDataLen);
+  void getFlavorData(in nsITransferable aTransferable, in string aFlavor, out nsISupports aData);
 };
 
 
diff --git a/widget/nsTransferable.cpp b/widget/nsTransferable.cpp
index 5d722a88b155..255484517631 100644
--- a/widget/nsTransferable.cpp
+++ b/widget/nsTransferable.cpp
@@ -270,9 +270,8 @@ nsTransferable::GetTransferData(const char* aFlavor,
     // Do we have a (lazy) data provider?
     if (nsCOMPtr<nsIFlavorDataProvider> dataProvider =
           do_QueryInterface(dataBytes)) {
-      uint32_t len;
       rv = dataProvider->GetFlavorData(this, aFlavor,
-                                       getter_AddRefs(dataBytes), &len);
+                                       getter_AddRefs(dataBytes));
       if (NS_FAILED(rv)) {
         dataBytes = nullptr;
         // The provider failed, fall into the converter code below.
@@ -298,11 +297,10 @@ nsTransferable::GetTransferData(const char* aFlavor,
         data.GetData(getter_AddRefs(dataBytes));
 
         // Do we have a (lazy) data provider?
-        uint32_t len;
         if (nsCOMPtr<nsIFlavorDataProvider> dataProvider =
               do_QueryInterface(dataBytes)) {
           rv = dataProvider->GetFlavorData(this, aFlavor,
-                                           getter_AddRefs(dataBytes), &len);
+                                           getter_AddRefs(dataBytes));
           if (NS_FAILED(rv)) {
             // Give up.
             return rv;
@@ -310,7 +308,7 @@ nsTransferable::GetTransferData(const char* aFlavor,
         }
 
         uint32_t dataLen;
-        return mFormatConv->Convert(data.GetFlavor().get(), dataBytes, len,
+        return mFormatConv->Convert(data.GetFlavor().get(), dataBytes, 0,
                                     aFlavor, aData, &dataLen);
       }
     }