When a program no longer accepts user input and does not seem to be performing any actions, it may be hanging. A program that is hanging may be stuck in a situation from which it cannot escape. Other terms for hanging are "freezing" or "not responding".

• A hanging program is different from a program that has crashed; a crash ends the program.
• A hanging program does not respond to your actions. In other situations, Firefox responds to your menu and button actions but fails to load any websites.

This article describes different situations in which Firefox may hang, and what you can do to correct the problem and prevent it from happening in the future. To resolve hanging problems not specifically mentioned in this article, see Basic Troubleshooting.

Table Of Contents

• Hang loading first window
• Hang loading every window
• Hang downloading files or saving images
• Hang opening the History menu or the History sidebar
• Hang loading websites
• Automatic proxy configuration file
• Duplicate Session Restore files
• Plugins
• Hang switching tabs
• Hang after prolonged use
• Hang deleting bookmarks folder
• Hang at exit

Hang loading every window

The SwitchProxy Tool extension checks for updates each time a new window is opened. This is a known issue.

If you use SwitchProxy Tool, you can disable it to see if hanging is prevented:

1. At the top of the Firefox windowOn the menu bar, click the Tools menu and then select Add-ons. The Add-ons dialog appears.
2. Select the Extensions panel. The list of installed extensions is displayed.
3. Select SwitchProxy Tool.
4. Click Disable.
5. From the menu at the top of the Firefox windowbar, select FileFirefox and then select the ExitQuit FirefoxQuit menu item.
6. Restart Firefox. Open several new windows to see if Firefox no longer hangs.

Hang downloading files or saving images

Firefox may hang when downloading files if your download history has grown too large. To fix this issue, the following steps clear the download history:

1. At the top of the Firefox windowOn the menu bar, click the Tools menu and then select Clear Private Data.... The Clear Private Data dialog appears.
2. Deselect all boxes except Download History.
3. Click Clear Private Data Now. The download history is cleared.
4. Download some sample files to see if the hanging has stopped.

Hang opening the History menu or the History sidebar

Firefox may hang when using the Go menu, History sidebar, or other features if your browsing history has grown too large. To fix this issue, the following steps clear the browsing history:

1. At the top of the Firefox windowOn the menu bar, click the Tools menu and then select Clear Private Data.... The Clear Private Data dialog appears.
2. Deselect all boxes except Browsing History.
3. Click Clear Private Data Now. The browsing history is cleared.
4. With the browsing history cleared, Firefox features such as the Go menu and the History sidebar should perform faster.

To prevent a recurrence of this issue, you can configure Firefox to retain a smaller browsing history:

1. At the top of the Firefox windowOn the menu bar, click on the ToolsFirefoxEdit menu, and select Options...Preferences....
2. Select the Privacy panel.
3. In the Keep my history for at least XX days text box, enter a value that is less than the current one. This value defines the number of days that Firefox retains browsing history; a lower figure should result in less retained browsing history.
4. Click OKClose the preferences window.

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. At the top of the Firefox windowOn the menu bar, click on the ToolsFirefoxEdit menu, and select 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 be slow to respond or hang if multiple copies of its Session Restore file have been created:

1. From the menu at the top of the Firefox windowbar, select FileFirefox and then select the ExitQuit FirefoxQuit menu item.
2. Open the Firefox profile folder.
   • To find your profile folder, see Profiles.
3. Locate and delete the sessionstore.js file and any copies, such as sessionstore-1.js, sessionstore-2.js.

Plugins

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 Troubleshooting plugins 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. When you exit the program, Firefox can remember your open windows and tabs. When you restart Firefox, you can optionally reload those windows and tabs.

To enable Session Restore:

1. At the top of the Firefox windowOn the menu bar, click on the ToolsFirefoxEdit menu, and select Options...Preferences....
2. Click the Main icon.
3. From the When Firefox starts drop-down, select Show my windows and tabs from last time.
4. Click OKClose the preferences window.
5. Firefox is now configured to remember your windows and tabs. You can close Firefox without losing the currently opened web pages, which may prevent Firefox from hanging.

Hang at exit

Sometimes when you close Firefox, it may stop responding and remain in memory, even though no Firefox windows are open.

When you next start Firefox, you may see problems in the new session, such as missing bookmarks or history and a blank Firefox window, which are resolved when you end all Firefox processes or restart the computer and then reopen Firefox. Other times, Firefox will not open at all and you will 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 Firefox will reopen. (See Firefox is already running but is not responding for other causes and solutions.)

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

• Problematic extensions, including AVG Safe Search, PicLens, and Skype Extension for Firefox, can cause the problem, which can be fixed by disabling or uninstalling the extension. See Troubleshooting extensions and themes for more information.

• 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 Java, disable the Java plugin by clearing the "Enable Java" checkbox in Firefox (see Using the Java plugin with Firefox for details).

Based on information from Firefox hangs (mozillaZine KB)