Firefox's about:config page is a direct interface to the browser's preference system — hundreds of settings not exposed in the regular UI. Here's a practical guide for power users.
Opening about:config
Type about:config in the address bar. Firefox shows a warning about voiding your warranty (click "Accept the Risk and Continue"). You're now in the preference editor.
Use the search bar at the top to filter preferences. You can add, modify, or reset any preference.
Essential Tweaks
Performance
gfx.webrender.all — Force-enable WebRender GPU compositor. Default is auto-detected. Set to true if your GPU supports it but it's disabled.
gfx.webrender.software — Use software WebRender if GPU WebRender causes issues.
browser.tabs.unloadOnLowMemory — Automatically unload inactive tabs when RAM is low. Default false on desktop.
browser.sessionstore.interval — How often (in ms) Firefox saves your session. Default 15000 (15 seconds). Can increase to 60000 to reduce disk I/O.
Privacy
privacy.firstparty.isolate — First-party isolation. Isolates cookies, cache, and other state per site. Can break some SSO. Default false.
privacy.resistFingerprinting — Reduces fingerprinting by lying to sites about fonts, canvas, timezone, etc. Breaks some sites. Part of Tor Browser's approach.
network.cookie.cookieBehavior — Cookie handling. Values:
- 0: All cookies allowed
- 1: Block third-party from new sites
- 2: Block all cookies
- 4: Block all third-party cookies
- 5: Reject tracking cookies (default in newer Firefox)
geo.enabled — Geolocation. Set to false to disable entirely.
media.peerconnection.enabled — WebRTC. Setting to false prevents WebRTC IP leaks when using a VPN. May break video calls.
UI & Behavior
browser.tabs.tabMinWidth — Minimum tab width in pixels. Default 76. Lower it to show more tabs.
browser.urlbar.suggest.history — Whether address bar suggests from history. Default true.
browser.search.suggest.enabled — Search suggestions in address bar. Default true.
dom.event.contextmenu.enabled — Right-click context menu. Sites can disable the right-click menu with JS; this setting ignores that.
layout.css.devPixelsPerPx — Global UI scale factor. Default -1 (use OS setting). Set to 1.5 for 150% scaling on Wayland or HiDPI without OS support.
browser.newtabpage.enabled — Show the Firefox home page on new tab. Set to false for a blank new tab.
Network
network.dns.disablePrefetch — DNS prefetching. Firefox prefetches DNS for links on the current page. Set to true to disable.
network.http.max-connections — Max simultaneous HTTP connections. Default 900.
network.http.pipelining — HTTP pipelining. Generally left at default.
network.prefetch-next — Prefetch pages Firefox thinks you'll visit. Set to false if you don't want this.
Developer
devtools.chrome.enabled — Enable browser chrome debugging in DevTools. Required for about:devtools-toolbox.
browser.dom.window.dump.enabled — Enable dump() for console output from chrome JS.
javascript.options.strict — Enable strict mode for all JS (developer use).
Resetting Preferences
To reset a preference to its default value: right-click it → "Reset" (or click the reset arrow on the right).
To reset all preferences: don't manually delete all of them. Instead, close Firefox, navigate to your profile folder, and delete prefs.js. Firefox recreates it from defaults on next launch.
Find your profile folder: about:support → Profile Directory → Open Directory.
User.js
For persistent tweaks that survive Firefox's preference resets, use user.js:
- Navigate to your Firefox profile directory
- Create a file named
user.js - Add preferences in this format:
user_pref("privacy.firstparty.isolate", true);
user_pref("browser.tabs.tabMinWidth", 50);
Firefox reads user.js on every startup and applies these settings. This means Firefox can't override them through updates — useful for settings that occasionally get reset.
Popular curated user.js configurations: arkenfox/user.js for privacy-focused tweaks.
Managing Sessions with about:config
One relevant preference: browser.sessionstore.max_tabs_undo — how many closed tabs are kept for ctrl+shift+T. Default 25.
For more comprehensive session management (saving named sessions, restoring specific tab sets without about:config), Tab Manager & Session Saver handles this at the extension level — no about:config required.
about:config gives you fine-grained control over Firefox's internals. Start with a few targeted changes rather than applying a huge user.js file — that makes it easier to diagnose if something breaks.
Top comments (0)