--- a/toolkit/components/xulstore/XULStore.js
+++ b/toolkit/components/xulstore/XULStore.js
@@ -139,17 +139,17 @@ XULStore.prototype = {
           this.setValue(docURI, id, attr.ValueUTF8, value.Value);
         }
       }
     }
   },
 
   readFile: function() {
     const MODE_RDONLY = 0x01;
-    const FILE_PERMS  = 0600;
+    const FILE_PERMS  = 0o600;
 
     let stream = Cc["@mozilla.org/network/file-input-stream;1"].
                  createInstance(Ci.nsIFileInputStream);
     let json = Cc["@mozilla.org/dom/json;1"].createInstance(Ci.nsIJSON);
     try {
       stream.init(this._storeFile, MODE_RDONLY, FILE_PERMS, 0);
       this._data = json.decodeFromStream(stream, stream.available());
     } catch(e) {