Firefox has a rich set of about: pages — internal pages that expose settings, debugging tools, and system information not accessible from the normal UI. Most Firefox users don't know most of them exist.
The Essential about: Pages
about:config
The advanced settings editor. Every tweakable Firefox setting lives here.
- Search any setting by name
- Double-click boolean to toggle, double-click string/number to edit
- Changed settings appear bold
- Right-click → Reset to restore default
Warning: Changing the wrong settings can break Firefox. Stick to settings you understand.
about:preferences (= about:settings)
The normal Settings page. Same as clicking the hamburger menu → Settings.
about:profiles
Manage Firefox profiles. Multiple profiles = completely separate Firefox instances with different settings, extensions, history, and accounts.
Create a new profile here, or switch between existing ones. Open Profile Folder button is the fastest way to find your Firefox data on disk.
about:support (= about:troubleshooting)
Comprehensive info page for debugging:
- Firefox version and build info
- Operating system details
- Profile path (with Open Folder button)
- Installed extensions (name, version, active/disabled)
- Modified preferences (everything you've changed from default)
- Graphics info (GPU, WebGL, hardware acceleration status)
- Media capabilities (codecs, DRM status)
- Security section (certificate issues)
Use when: Something is broken and you need to diagnose. "Copy text to clipboard" button at top gives a plain-text version to paste in a bug report.
about:addons
Extension manager. Same as clicking the puzzle piece icon.
Manage installed extensions, themes, and plugins. Each extension page shows permissions, storage used, and options.
about:performance
Live performance monitor. Shows:
- Memory usage by tab
- CPU usage by tab
- Background processes
- Extension overhead
Useful for: Finding which tab or extension is eating memory. The "Close" link next to a heavy tab closes it immediately.
about:memory
Detailed memory analysis. More technical than about:performance.
- "Measure" button takes a snapshot of current memory usage
- Shows memory breakdown by process, compartment, and object type
- "Minimize memory usage" button forces garbage collection
Use when: Firefox is using more memory than expected and you want to diagnose what's holding it.
about:networking
Network diagnostic page:
- DNS: Shows DNS cache and DoH settings
- Sockets: Active socket connections
- HTTP: HTTP/3 and HTTP/2 status
- DNS: Resolver configuration and cache
Useful for diagnosing whether DoH is actually working.
about:telemetry
Shows exactly what telemetry Firefox collects about your session. Every metric Firefox sends (or would send) to Mozilla is listed here.
If you're concerned about what Firefox reports: go here and read it. It's the actual data, not a summary.
about:crashes
Crash report history. Firefox crash reporter stores recent crashes here.
If Firefox has been crashing: open this page to see crash IDs, then submit them to Mozilla Crash Reports for analysis.
about:logins
Password manager (Firefox Lockwise). Manage saved usernames and passwords:
- Search by site
- Edit or delete saved credentials
- Export as CSV
- Import from CSV
No third-party app needed — this is your password vault.
about:policies
Enterprise policy viewer. Shows if any managed policies are applied to your Firefox (common on work computers where IT sets browser policies).
If Firefox is blocking certain settings or sites: check here to see if your organization has locked them down.
about:robots
Easter egg. Just for fun.
about:blank
An empty page with no content. Useful as new tab page if you prefer it (Settings → Home → Homepage → Custom URLs → about:blank).
about:newtab
The New Tab page. Same as opening Ctrl+T.
Customizable in Settings → Home.
about:home
Firefox's start page. Same as the new tab page in modern Firefox.
Developer-Specific about: Pages
about:debugging
Extension and service worker debugging:
- Debug installed extensions (access background scripts, inspect UI)
- List active service workers
- Remote debugging connections (debug Firefox on another device or tab)
For extension developers: This is where you load temporary extensions for development.
about:serviceworkers
Service worker manager. Shows all active service workers and allows unregistering them.
If a PWA is misbehaving, unregistering its service worker from here and refreshing often fixes it.
about:cache
HTTP cache viewer. Shows what Firefox has cached locally.
- List all cached entries
- Search for specific URLs
- View headers and cache metadata for each entry
- Delete specific cached items
about:certificate
Since Firefox 83: View TLS certificate details for any website.
Instead of clicking the lock icon and navigating menus: go to about:certificate?cert=[base64] or reach it from the certificate viewer in the security panel.
Quick Reference Table
| Page | What It Shows |
|---|---|
| about:config | All settings (advanced) |
| about:support | Diagnostics, system info, modified prefs |
| about:performance | Tab/extension CPU and memory usage |
| about:memory | Detailed memory breakdown |
| about:profiles | Manage Firefox profiles |
| about:addons | Extension manager |
| about:logins | Password manager |
| about:networking | Network/DNS diagnostics |
| about:telemetry | What data Firefox collects |
| about:crashes | Crash report history |
| about:debugging | Extension/service worker debugger |
| about:cache | HTTP cache browser |
| about:policies | Enterprise policy viewer |
Useful about:config Settings Worth Knowing
While you're in about:config, these are commonly useful tweaks:
| Setting | Description |
|---|---|
browser.tabs.tabMinWidth |
Minimum tab width in pixels (default: 76) |
network.http.max-connections |
Max parallel HTTP connections |
privacy.resistFingerprinting |
Enable fingerprinting resistance |
ui.prefersReducedMotion |
Force reduced motion (0=auto, 1=reduce, 2=normal) |
layout.css.devPixelsPerPx |
DPI scaling (-1 = auto, 2.0 = 2x) |
media.autoplay.default |
Autoplay policy (0=allow, 1=block, 5=block with exception) |
browser.urlbar.suggest.history |
Show history in address bar suggestions |
browser.sessionstore.interval |
How often session is saved (ms, default 15000) |
Always search for the exact setting name in about:config rather than relying on documentation (settings can change between versions).
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