Firefox about:config: The Power User Settings Guide

Firefox's about:config page provides direct access to the browser's settings, hiding hundreds of options from the regular user interface. Here's a guide for power users to navigate this feature.

To access about:config, type the phrase into the address bar and press Enter. You'll be warned about potential risks before being taken to the preference editor.

Use the search bar at the top of the page to filter through these settings. You can modify, add, or reset any preference as needed.

Several important tweaks can enhance performance:

- gfx.webrender.all: Enable this to force-enable the WebRender GPU compositor, even if it's disabled by default. Not all GPUs support it.

- browser.tabs.unloadOnLowMemory: Automatically unload inactive tabs when the system runs low on RAM. This can free up memory but may cause tabs to reload when reopened.

- privacy.firstparty.isolate: Isolate cookies, cache, and other state for each website. This enhances privacy but may break some single sign-on (SSO) solutions.

- privacy.resistFingerprinting: Reduces browser fingerprinting by lying to websites about details like fonts and timezones. However, it can break some sites.

To reset a preference to its default value, right-click it and select Reset. To reset all preferences, delete the prefs.js file from your Firefox profile folder and then relaunch the browser. This ensures Firefox recreates the settings file from its defaults.

User.js is another tool for persisting changes. By adding preferences in this file, you can ensure settings remain even after Firefox updates. Popular user.js configurations focus on privacy, such as arkenfox/user.js.

Managing sessions also relies on about:config. For example, browser.sessionstore.max_tabs_undo controls how many closed tabs are kept for easy reopening using Ctrl+Shift+T. Other preferences, like network.dns.disablePrefetch, let you disable DNS prefetching for more control over data collection.