on Windows and Linux, they go into the same directory where Firefox is installed
   on macOS, they go into the Contents/Resources directory of the Firefox.app 

   autoconfig.cfg and autoconfig.js need to start with a comment line (//)
   autoconfig.js needs to use Unix line endings (LF instead of CR/LF) 

   https://support.mozilla.org/en-US/kb/customizing-firefox-using-autoconfig 

//
pref("general.config.filename", "autoconfig.cfg");
pref("general.config.obscure_value", 0);
pref("general.config.sandbox_enabled", false); // disable sandbox to allow privileged JavaScript

let {classes:Cc, interfaces:Ci, manager:Cm, utils:Cu} = Components;
var Services = globalThis.Services || ChromeUtils.import("resource://gre/modules/Services.jsm").Services;

function ConfigJS() { Services.obs.addObserver(this, 'chrome-document-global-created', false); }
ConfigJS.prototype = {
 observe: function (aSubject) { aSubject.addEventListener('DOMContentLoaded', this, {once: true}); },
 handleEvent: function (aEvent) {
  let document = aEvent.originalTarget;
  let window = document.defaultView;
  let location = window.location;
  if (/^(chrome:(?!\/\/(global\/content\/commonDialog|browser\/content\/webext-panels)\.x?html)|about:(?!blank))/i.test(location.href)) {
   if (window._gBrowser) {
     let showPlaces = ["AllBookmarks","BookmarksMenu","BookmarksToolbar","UnfiledBookmarks"][1];
     elm = document.getElementById("Browser:ShowAllBookmarks");
     if (elm) {
      elm.setAttribute("oncommand", "PlacesCommandHook.showPlacesOrganizer('"+showPlaces+"')");
     }
   }
  }
 }
};
if (!Services.appinfo.inSafeMode) { new ConfigJS(); }

When I click Bookmarks > Manage Bookmarks I'm taken to Other Bookmarks where I never store anything. I'd delete it if I could but it doesn't appear to be an option, so instead I'd like to taken directly to Bookmarks Menu. I came across this post from just over 4 years ago which sounded like it's exactly what I want, but it doesn't work. Are there any changes anyone can suggest that would allow it to work in 2026? https://support.mozilla.org/en-US/questions/1373437 You can use the autoconfig.cfg file in the Firefox installation folder to initialize (set/lock) preferences and run privileged JavaScript code. In this case code to open the Library with the Bookmarks Menu folder selected. You can modify the showPlaces variable to open any of the four possible root folders (in this case [1]). To use Autoconfig, place two files into the Firefox installation directory. on Windows and Linux, they go into the same directory where Firefox is installed on macOS, they go into the Contents/Resources directory of the Firefox.app The autoconfig.js file that specifies to use autoconfig.cfg is placed into the "defaults\pref" directory where the channel-prefs.js file is located. The autoconfig.cfg file is placed at the top level of the Firefox directory. autoconfig.cfg and autoconfig.js need to start with a comment line (//) autoconfig.js needs to use Unix line endings (LF instead of CR/LF) See also: https://support.mozilla.org/en-US/kb/customizing-firefox-using-autoconfig Content of autoconfig.js // pref("general.config.filename", "autoconfig.cfg"); pref("general.config.obscure_value", 0); pref("general.config.sandbox_enabled", false); // disable sandbox to allow privileged JavaScript Content of autoconfig.cfg // first line in autoconfig.cfg is a comment line try { let {classes:Cc, interfaces:Ci, manager:Cm, utils:Cu} = Components; var Services = globalThis.Services || ChromeUtils.import("resource://gre/modules/Services.jsm").Services; function ConfigJS() { Services.obs.addObserver(this, 'chrome-document-global-created', false); } ConfigJS.prototype = { observe: function (aSubject) { aSubject.addEventListener('DOMContentLoaded', this, {once: true}); }, handleEvent: function (aEvent) { let document = aEvent.originalTarget; let window = document.defaultView; let location = window.location; if (/^(chrome:(?!\/\/(global\/content\/commonDialog|browser\/content\/webext-panels)\.x?html)|about:(?!blank))/i.test(location.href)) { if (window._gBrowser) { let showPlaces = ["AllBookmarks","BookmarksMenu","BookmarksToolbar","UnfiledBookmarks"][1]; elm = document.getElementById("Browser:ShowAllBookmarks"); if (elm) { elm.setAttribute("oncommand", "PlacesCommandHook.showPlacesOrganizer('"+showPlaces+"')"); } } } } }; if (!Services.appinfo.inSafeMode) { new ConfigJS(); } } catch(e) {Cu.reportError(e);}