diff --git a/browser/app/profile/firefox.js b/browser/app/profile/firefox.js
index e52f0c107170..2e8218ce8958 100644
--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -102,10 +102,10 @@ pref("app.update.log", false);
 pref("app.update.backgroundMaxErrors", 10);
 
 // The aus update xml certificate checks for application update are disabled on
-// Windows since the mar signature check which is currently only implemented on
-// Windows is sufficient for preventing us from applying a mar that is not
+// Windows and Mac OS X since the mar signature check are implemented on these
+// platforms and is sufficient to prevent us from applying a mar that is not
 // valid.
-#ifdef XP_WIN
+#if defined(XP_WIN) || defined(XP_MACOSX)
 pref("app.update.cert.requireBuiltIn", false);
 pref("app.update.cert.checkAttributes", false);
 #else