Firefox hangs

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.

Hang loading first window

A Firefox hang while loading the first browser window may be caused by hyper-threading. A feature on some Intel Pentium 4 processors, hyper-threading is designed to improve performance, but it can also cause Firefox to hang.
If your computer has an Intel Pentium 4 processor and you use Windows 2000 and XP, you can disable hyper-threading for Firefox:

1. Right-click the shortcut icon you use to start Firefox.
2. Select Properties.
3. Select the Compatibility icon.
4. Select Run this program in compatibility mode.
5. In the drop-down for compatibility mode, select Windows 98/Windows ME.
6. Click OK.
7. Restart Firefox to see if the hanging has gone away.

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.

Firefox 3:

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.

Firefox 2:

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 Remember visited pages for the last 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.

Linux, Windows:

Hang switching tabs

Spybot S&D's "Immunize" feature can add a large number of entries into the Firefox cookie configuration file. This can cause slowdown while switching tabs.

1. Open Spybot S&D
2. Click the Immunize icon on the left side of the window.
3. Right-click in the Immunization list and choose Deselect all from the context menu.
4. In the Firefox section, put a check mark next to each item.
5. Click Undo at the top of the window.

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 OK.
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.

Firefox 3:

Hang deleting bookmarks folder

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