--- a/widget/cocoa/nsClipboard.mm
+++ b/widget/cocoa/nsClipboard.mm
@@ -594,16 +594,18 @@ nsClipboard::PasteboardDictFromTransfera
 
       NSString* str = nsCocoaUtils::ToNSString(fileURI);
       NSArray* fileList = [NSArray arrayWithObjects:str, nil];
       [pasteboardOutputDict setObject:fileList forKey:NSFilenamesPboardType];
     }
     else if (flavorStr.EqualsLiteral(kFilePromiseMime)) {
       [pasteboardOutputDict setObject:[NSArray arrayWithObject:@""]
                                forKey:(NSString*)kPasteboardTypeFileURLPromise];
+      [pasteboardOutputDict setObject:[NSArray arrayWithObject:@""]
+                               forKey:(NSString*)kPasteboardTypeFilePromiseContent];
     }
     else if (flavorStr.EqualsLiteral(kURLMime)) {
       uint32_t len = 0;
       nsCOMPtr<nsISupports> genericURL;
       rv = aTransferable->GetTransferData(flavorStr, getter_AddRefs(genericURL), &len);
       nsCOMPtr<nsISupportsString> urlObject(do_QueryInterface(genericURL));
 
       nsAutoString url;