How to Fix Firefox Not Responding on PC and Mac

Firefox freezing or showing a “Not Responding” message can disrupt your browsing, but in most cases the fix is straightforward. This guide walks you through the most effective solutions for both Windows and macOS, from simple restarts to deeper profile troubleshooting.

What You’ll Need

Access to your computer’s Task Manager (Windows) or Activity Monitor (Mac)
Administrator or standard user account (no special privileges required for most steps)
Your Firefox bookmarks and passwords backed up (optional but recommended before major steps)

Step-by-Step

Force-quit Firefox and restart it. On Windows, press Ctrl+Shift+Esc to open Task Manager, select Firefox under “Processes,” and click “End Task.” On Mac, press Cmd+Option+Esc, select Firefox, and click “Force Quit.” Then reopen Firefox. This clears a temporary glitch.
Check for multiple Firefox processes. After restarting, open Task Manager (Windows) or Activity Monitor (Mac) again. If you see many Firefox processes using high CPU or memory, close some tabs or extensions. A single tab can spawn several processes, but if one is stuck at 100% CPU, it may be the culprit.
Disable hardware acceleration. Click the menu button (three horizontal lines) â†’ Settings â†’ General â†’ scroll to “Performance.” Uncheck “Use recommended performance settings” and then uncheck “Use hardware acceleration when available.” Restart Firefox. This often resolves rendering-related freezes, especially on Windows with older graphics drivers.
Update Firefox. Click the menu â†’ Help â†’ About Firefox. The About window will check for updates and install them automatically. Restart Firefox after updating. An outdated version can have bugs that cause freezes.
Clear the cache and cookies. Go to Settings â†’ Privacy & Security â†’ Cookies and Site Data â†’ click “Clear Data.” Ensure both boxes are checked, then click Clear. This removes corrupted cached files that may cause pages to hang.
Run Firefox in Troubleshoot Mode. Click the menu â†’ Help â†’ Troubleshoot Mode (or hold Shift while starting Firefox on Windows, or Option while starting on Mac). This starts Firefox with all extensions disabled and hardware acceleration off. If Firefox runs smoothly here, an extension or theme is likely causing the problem.
Disable or remove problematic extensions. If Troubleshoot Mode works, go to the menu â†’ Add-ons and Themes â†’ Extensions. Disable all extensions, then re-enable them one by one, restarting Firefox after each, until you find the one that causes the freeze. Remove or update that extension.
Refresh Firefox. If the problem persists, go to the menu â†’ Help â†’ More Troubleshooting Information â†’ click “Refresh Firefox.” This resets Firefox to its default state while keeping your bookmarks, passwords, and open tabs. It disables extensions and clears some preferences. Confirm the refresh and restart Firefox.
Check for malware or adware. On Windows, run a full scan with Windows Defender or a reputable antivirus. On Mac, run Malwarebytes or the built-in malware removal tool. Malicious software can hijack Firefox and cause it to freeze.
Reinstall Firefox. If nothing else works, uninstall Firefox (Windows: Settings â†’ Apps; Mac: drag Firefox to the Trash). Then download the latest version from the official Mozilla website and install it. Your profile data is usually preserved, but to be safe, back up your bookmarks and passwords first.

Common Mistakes

Skipping the force-quit. Just closing the window may not kill all background processes. Always use Task Manager or Activity Monitor to fully quit Firefox.
Ignoring the profile. Many users reinstall Firefox but keep the same corrupted profile. Refreshing or creating a new profile is often necessary.
Not updating graphics drivers. Hardware acceleration relies on your GPU drivers. Outdated drivers can cause freezes even if Firefox is up to date.
Assuming all extensions are safe. An extension that worked for years can become incompatible after a Firefox update. Always test with Troubleshoot Mode.
Clearing only the cache. Cookies and site data can also be corrupted. Clear both for a more thorough fix.

Tips

Use the built-in task manager. Firefox has its own Task Manager (Shift+Esc) that shows which tabs or extensions are using the most memory. Open it when Firefox starts to slow down.
Keep a reasonable number of tabs open. Hundreds of tabs can exhaust memory, especially on systems with 8GB RAM or less. Use bookmark folders or a tab suspender extension.
Regularly update Firefox and your OS. Updates often include performance fixes and memory leak patches.
Create a new profile for testing. You can create a separate Firefox profile (via about:profiles) to test if the issue is profile-related without losing your main data.
Disable automatic extension updates if they cause problems. Go to Settings â†’ General â†’ Firefox Updates and choose to check for updates but let you choose to install them. This gives you control.

Troubleshooting

If the steps above don’t resolve the issue, try these additional checks:

Check for system resource exhaustion. Open Task Manager or Activity Monitor and look at overall memory and CPU usage. If your system is at 100% memory, close other applications or restart your computer.
Check for conflicting software. Some security suites or VPN software can interfere with Firefox. Temporarily disable them to see if the freezes stop.
Inspect the profile folder for corruption. Navigate to your profile folder (type about:support in Firefox, then click “Open Folder” next to Profile Folder). Look for files with .corrupt extensions or large sessionstore files. You can rename sessionstore.jsonl to sessionstore.old to reset your session, but this will lose open tabs.
Try a different user account. Create a new user account on your OS and try Firefox there. If it works, your main account’s settings or files may be causing the issue.
Check for disk errors. On Windows, run chkdsk; on Mac, run First Aid in Disk Utility. Corrupted disk sectors can cause Firefox to hang when reading cached files.

Frequently Asked Questions

Why does Firefox keep saying “Not Responding” when I open it?

This often happens due to a corrupted profile, an incompatible extension, or a conflict with hardware acceleration. Start by running Troubleshoot Mode to isolate the cause.

Will refreshing Firefox delete my bookmarks and passwords?

No, refreshing Firefox keeps your bookmarks, passwords, and open tabs. It only removes extensions and resets some preferences.

How do I know if an extension is causing the problem?

Run Firefox in Troubleshoot Mode. If it works fine, disable all extensions, then re-enable them one by one, restarting Firefox after each, to identify the culprit.

Can I recover my session if Firefox crashes?

Yes, Firefox usually restores your previous session after a crash. If it doesn’t, you can go to History â†’ Recently Closed Tabs, or use the about:sessionrestore page to restore your session manually.

Is there a difference between fixing Firefox on Windows and Mac?

The steps are largely the same, but the force-quit method and some menu names differ. The core troubleshooting (extensions, cache, profile) is identical.

What if Firefox still freezes after reinstalling?

If reinstalling doesn’t help, the issue may be with your profile data. Create a new profile via about:profiles and test it. If that works, you can migrate your bookmarks and passwords from the old profile.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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