diff --git a/toolkit/content/PrivateBrowsingUtils.jsm b/toolkit/content/PrivateBrowsingUtils.jsm
index 52528d6c98e..f54396adfb5 100644
--- a/toolkit/content/PrivateBrowsingUtils.jsm
+++ b/toolkit/content/PrivateBrowsingUtils.jsm
@@ -27,8 +27,13 @@ this.PrivateBrowsingUtils = {
   },
 
   get permanentPrivateBrowsing() {
-    return gTemporaryAutoStartMode ||
-           Services.prefs.getBoolPref(kAutoStartPref, false);
+    try {
+      return gTemporaryAutoStartMode ||
+             Services.prefs.getBoolPref(kAutoStartPref);
+    } catch (e) {
+      // The pref does not exist
+      return false;
+    }
   },
 
   // These should only be used from internal code