--- a/xpcom/io/CocoaFileUtils.mm
+++ b/xpcom/io/CocoaFileUtils.mm
@@ -1,20 +1,26 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 // vim:set ts=2 sts=2 sw=2 et cin:
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "CocoaFileUtils.h"
+#include "nsCocoaFeatures.h"
 #include "nsCocoaUtils.h"
 #include <Cocoa/Cocoa.h>
 #include "nsObjCExceptions.h"
 #include "nsDebug.h"
 
+// Need to cope with us using old versions of the SDK and needing this on 10.10+
+#if !defined(MAC_OS_X_VERSION_10_10) || (MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_10)
+const CFStringRef kCFURLQuarantinePropertiesKey = CFSTR("NSURLQuarantinePropertiesKey");
+#endif
+
 namespace CocoaFileUtils {
 
 nsresult RevealFileInFinder(CFURLRef url)
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
 
   if (NS_WARN_IF(!url))
     return NS_ERROR_INVALID_ARG;
@@ -188,19 +194,26 @@ void AddOriginMetadataToFile(const CFStr
 void AddQuarantineMetadataToFile(const CFStringRef filePath,
                                  const CFURLRef sourceURL,
                                  const CFURLRef referrerURL) {
   CFURLRef fileURL = ::CFURLCreateWithFileSystemPath(kCFAllocatorDefault,
                                                      filePath,
                                                      kCFURLPOSIXPathStyle,
                                                      false);
 
+  // The properties key changed in 10.10:
+  CFStringRef quarantinePropKey;
+  if (nsCocoaFeatures::OnYosemiteOrLater()) {
+    quarantinePropKey = kCFURLQuarantinePropertiesKey;
+  } else {
+    quarantinePropKey = kLSItemQuarantineProperties;
+  }
   CFDictionaryRef quarantineProps = NULL;
   Boolean success = ::CFURLCopyResourcePropertyForKey(fileURL,
-                                                      kLSItemQuarantineProperties,
+                                                      quarantinePropKey,
                                                       &quarantineProps,
                                                       NULL);
 
   // If there aren't any quarantine properties then the user probably
   // set up an exclusion and we don't need to add metadata.
   if (!success || !quarantineProps) {
     ::CFRelease(fileURL);
     return;
@@ -238,17 +251,17 @@ void AddQuarantineMetadataToFile(const C
   }
 
   if (!::CFDictionaryGetValue(mutQuarantineProps, kLSQuarantineDataURLKey)) {
     ::CFDictionarySetValue(mutQuarantineProps, kLSQuarantineDataURLKey, sourceURL);
   }
 
   // Set quarantine properties on file.
   ::CFURLSetResourcePropertyForKey(fileURL,
-                                   kLSItemQuarantineProperties,
+                                   quarantinePropKey,
                                    mutQuarantineProps,
                                    NULL);
 
   ::CFRelease(fileURL);
   ::CFRelease(mutQuarantineProps);
 }
 
 } // namespace CocoaFileUtils