Firefox about:config Settings Worth Changing (With Explanations)

Firefox's about:config page exposes hundreds of hidden settings. Most guides give you a list to copy-paste without explaining what each does. Here are the ones worth changing, with honest explanations of the trade-offs.

To access: type about:config in your address bar, accept the warning.

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Performance

gfx.webrender.all

Default: false (on some hardware)
Set to: true

WebRender is Firefox's GPU-accelerated compositor. On most modern GPUs it's faster. On some older GPUs it causes issues. If your Firefox scrolling feels sluggish: enable this, restart Firefox, see if it improves.

Rollback: set back to false if you see visual glitches.

network.http.max-connections

Default: 900
Set to: 1500 (or higher)

Maximum concurrent HTTP connections Firefox will maintain. Increasing this can improve loading multiple assets at once on content-heavy sites. Diminishing returns past 2000.

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Privacy and Tracking

privacy.resistFingerprinting

Default: false
Set to: true

Randomizes a variety of browser fingerprinting APIs — canvas, AudioContext, timezone, screen resolution reported to sites. Makes your browser fingerprint less unique.

Trade-off: breaks some sites that rely on canvas fingerprinting for non-tracking purposes. Some web games and graphics demos may look wrong. Use Firefox's private windows (which already enable this) if you want it selectively.

privacy.trackingprotection.fingerprinting.enabled

Default: false
Set to: true

Blocks known fingerprinting scripts separately from content blocking. Less aggressive than resistFingerprinting, fewer breakages.

network.http.sendRefererHeader

Default: 2 (always send)
Set to: 0 (never send) or 1 (send only same-origin)

The HTTP Referer header tells sites where you came from. Setting to 0 means no site knows which link you clicked to arrive there. Some sites require this for authentication flows. Start with 1 (same-origin only) if you're unsure.

geo.enabled

Default: true
Set to: false

Disables the browser geolocation API entirely. Sites that ask for your location will get an error instead of a permission prompt. If you use location-based services, leave this enabled.

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Dark Mode

ui.systemUsesDarkTheme

Default: not set (inherits from OS)
Set to: 1 (force dark preference)

Tells Firefox to report prefers-color-scheme: dark to all websites regardless of your OS setting. Useful if you run your OS in light mode but want websites to use dark themes. Only affects sites that respect this CSS media query.

Note: this doesn't force dark mode on all sites — sites that ignore prefers-color-scheme won't change. For those, you need a browser extension like NightOwl.

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Tab and UI Behavior

browser.tabs.closeWindowWithLastTab

Default: true
Set to: false

Stops Firefox from closing the entire window when you close the last tab. Instead, it opens a new empty tab. Useful if you accidentally close your last tab and don't want the whole window to disappear.

browser.tabs.warnOnClose

Default: true
Set to: false (optional)

Disables the "close N tabs?" confirmation dialog when closing a window with multiple tabs. If you've set up session saving (via Firefox Sync or a tab manager extension), you don't need this safety net.

browser.backspace_action

Default: 0 (go back in history)
Set to: 2 (do nothing)

Setting 0 means the Backspace key navigates back. If you're typing in a form and accidentally press Backspace in the wrong context, this can navigate away and lose form data. Setting to 2 disables this behavior.

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Developer Tools

devtools.chrome.enabled

Default: false
Set to: true

Enables the Browser Toolbox, which lets you inspect Firefox's own UI elements (not just web pages). Useful for extension development or debugging Firefox UI issues.

browser.dom.window.dump.enabled

Default: false
Set to: true (if debugging)

Enables window.dump() in web content. Useful for extension developers debugging content scripts.

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What Not to Change

Some about:config settings are genuinely risky:

• network.websocket.enabled: Disabling this breaks many web applications
• security.tls.version.min: Don't lower TLS minimum version — you'll become vulnerable to downgrade attacks
• dom.storage.enabled: Disabling localStorage breaks most web apps

The settings above are lower risk. Always note what you changed so you can revert.