--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -97,20 +97,20 @@ pref("app.update.altwindowtype", "Browse
 pref("app.update.log", false);
 
 // The number of general background check failures to allow before notifying the
 // user of the failure. User initiated update checks always notify the user of
 // the failure.
 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
 // When |app.update.cert.requireBuiltIn| is true or not specified the
 // final certificate and all certificates the connection is redirected to before
 // the final certificate for the url specified in the |app.update.url|
 // preference must be built-in.
 pref("app.update.cert.requireBuiltIn", true);