When you select the categories you want shown in the autocomplete drop-down, either through the Options page or in about:config, your changes are saved to the '''prefs.js''' file. Those should of course be saved indefinitely. This article covers some reasons that the changes might be lost or overridden: [[How to fix preferences that won't save]]. Also beware of programs like Advanced SystemCare that roll back settings files to protect against unwanted changes -- they can't distinguish your changes from those made by others. You may need to disable surfing protection, home page protection, browser protection, etc., at least until your settings are finalized.