What do you mean with an update ? The about:config page shows all prefs that aren't hidden by default (i.e. Firefox may assume a default value and you would have to add the pref yourself to override this default). Each Firefox version has new prefs and some older prefs are no longer supported or deprecated. You shouldn't rely on that prefs keep working, especially if you notice a trashcan on a pref you modified in the past. WARNING: modifying prefs directly via the <b>about:config</b> page can sometimes break Firefox or cause strange behavior, and there is no guarantee that this will keep working in future Firefox releases, so be cautious with modifying prefs if you aren't sure you understand their purpose. You should only do this if you know what you're doing. You can possibly search the source code to get more info about a specific pref. You may have to leave the leading pref branch part. *https://searchfox.org/mozilla-release/source/