Firefox hangs or is not responding - How to fix

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  • Creator: scoobidiver
  • Comment: removed switchProxy, large history, Spybot sections (no longer applicable), fixed menu paths, reworded intro, added steps in P4 section, added After Session Restore section, simplified security software section, added summary & keywords
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When Firefox hangs, it no longer accepts user input and does not seem to be performing any actions, a "(Not Responding)" label is displayed in its title bars, and the mouse cursor becomes a wait cursor inside its windows. This article shows solutions to Firefox hanging problems depending on their reproducibility conditions.

To resolve hanging problems not specifically mentioned in this article, or if the suggested solutions do not solve the problem, see Troubleshoot and diagnose Firefox problems.

Hang loading first window

Computer with a Pentium 4 processor

A Firefox hang on computers with Intel Pentium 4 processors while loading the first browser window may be caused by "hyper-threading", a feature designed to improve performance.

If your computer has an Intel Pentium 4 processor and you use Windows 2000 and XP, you can disable hyper-threading for Firefox:

  1. Open the System Information window following steps in Description of Windows XP System Information (Msinfo32.exe) Tool at
  2. Make sure your processor is an Intel Pentium 4
    • If your processor is not an Intel Pentium 4, skip the next steps of this section.
  3. Right-click the shortcut icon you use to start Firefox.
  4. Select Properties.
  5. Select the Compatibility icon.
  6. Select Run this program in compatibility mode.
  7. In the drop-down for compatibility mode, select Windows 98/Windows ME.
  8. Click OK.
  9. Restart Firefox to see if the hanging has gone away.

After a session restore

If you have many tabs to restore, Firefox may hang while loading every websites. Try to use Tab Groups so that only websites in the visible tab group load first.

Hang downloading files or saving images

If Firefox hangs when you attempt to download a file or save an image, try these solutions:

Clear download history

Firefox may hang when downloading files if your download history has grown too large. To clear the download history:

  1. At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP), and then click DownloadsAt the top of the Firefox window, click on the Tools menu, and then click DownloadsOn the menu bar, click on the Tools menu, and then click DownloadsAt the top of the Firefox window, click on the Tools menu, and then click Downloads. The Downloads window will open.
  2. Click Clear List. The download history is cleared.
  3. Download some sample files to see if the hanging has stopped.

Choose a different download folder

Firefox may hang if the last download folder location (e.g. a shared volume or USB drive) is no longer available. To fix this:

  1. Click the menu button New Fx Menu and choose Options.Preferences.
  2. Select the General panel.
  3. In the Downloads pane, select Save files to and click the Browse button.
  4. In the Browse For Folder window, choose a new folder location.
  5. Close the about:preferences page. Any changes you've made will automatically be saved.

See if you are now able to download files or save images. If this works, you can go back to your Firefox settings, if you wish, and select Always ask me where to save my files.

Hang loading websites

Automatic proxy configuration file

If you're using an automatic proxy configuration file (PAC), Firefox may hang when you attempt to load sites that don't exist or that you haven't opened recently. To determine if you use an automatic proxy configuration file:

  1. Click the menu button New Fx Menu and choose Options.Preferences.
  2. Click the Advanced icon.
  3. Click the Network tab.
  4. Click Settings. The Connection Settings dialog appears.
  5. If Automatic proxy configuration URL is selected, you are using an automatic proxy configuration file. Do not disable this setting, which will prevent you from accessing the Internet. Instead, provide this link to your network administrator.
  6. Click Cancel.

Duplicate Session Restore files

Firefox may be slow to respond or hang if multiple copies of its Session Restore file have been created:

  1. Open your profile folder:

    Click the menu button New Fx Menu , click help Help-29 and select Troubleshooting Information. The Troubleshooting Information tab will open.

  2. Under the Application Basics section, click on Show FolderOpen FolderShow in FinderOpen Directory. A window with your profile filesfolder will open.
  3. Note: If you are unable to open or use Firefox, follow the instructions in Finding your profile without opening Firefox.

  4. Click the menu button New Fx Menu and then click ExitQuit Close 29 .
  5. Locate and delete the sessionstore.js file and any copies, such as sessionstore-1.js, sessionstore-2.js.

Turn off hardware acceleration

With some graphics card and graphics driver setups, Firefox may hang when using hardware acceleration. You can try turning off hardware acceleration to see if it fixes the problem.

  1. Click the menu button New Fx Menu and choose Options.Preferences.
  2. Select the Advanced panel and the General tab.
  3. Uncheck Use hardware acceleration when available.
  4. Click the menu button New Fx Menu and then click ExitQuit Close 29 .
  5. Start Firefox the way you normally do.

If the problem is no longer happening, then hardware acceleration was likely the cause. You can try updating your graphics drivers to see if that fixes it or simply run without hardware acceleration.


Sites that use plugins such as Java, Adobe Reader, or Flash can cause Firefox to hang. For information on troubleshooting plugins and on determining whether a plugin is causing your problem, see the Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems article.

Hang after prolonged use

Firefox may hang if left open for long periods of time. To fix the issue, restart Firefox.

If you regularly leave Firefox open so that you return to where you left off, you may want to use Firefox's Session Restore feature. For more information, see Configuring session restore.

Hang deleting bookmarks folder

Trying to delete a bookmarks folder that contains many bookmarks and multiple levels of sub-folders can cause Firefox to hang. To work around this problem, delete unwanted bookmark sub-folders in small steps.

Hang at exit

Sometimes when you close Firefox, it may stop responding and remain in memory, even though no Firefox windows are open. This can prevent Firefox from working properly the next time you open it or you may see a "Close Firefox" dialog box with the message, Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.. You must then end all Firefox processes or restart the computer before you can reopen Firefox. (See "Firefox is already running but is not responding" error message - How to fix it for other causes and solutions.)

If Firefox processes that remain in memory at exit are a recurring problem, try these solutions:

  • Sometimes Java applets can cause the Firefox process to persist after exit. Try updating Java to the latest version or, if you don't need the Java plugin, you can disable it from the Plugins panel of the Firefox Add-ons Manager. For more information, see Use the Java plugin to view interactive content on websites.
  • Interactions between certain Internet security software (firewall, antivirus software) is reported to cause the issue on some systems.

Closing Firefox properly

  1. Click the menu button New Fx Menu and then click ExitQuit Close 29 .
  2. Close any remaining dialog boxes or secondary windows such as the Downloads window or the Add-ons window.

Based on information from Firefox hangs (mozillaZine KB)