Using an autoconfig file to create bookmarks

I'm using an example provided by Mike Kaply to modify my autoconfig file to add bookmarks to users profiles. However, every time I launch FF, instead of the bookmarks being overwritten, I get an extra set. So, after 5 re-launches, I have 5 sets of the bookmarks I'm adding. Is there a way to prevent this? Here is the code I'm using: //Add bookmarks Components.utils.import("resource://gre/modules/Services.jsm"); var uri = Services.io.newURI("http://mike.kaply.com", null, null); var navBook = Components.classes["@mozilla.org/browser/nav-bookmarks-service;1"].getService(Components.interfaces.nsINavBookmarksService); //create new Folder var FolderId = navBook.createFolder(navBook.bookmarksMenuFolder, "New Folder", 0); //add bookmark to newly created folder navBook.insertBookmark(SCCCFolderId, uri, -1, "Mike's Blog");