When Firefox hangs, it stops responding to your clicks and keystrokes and doesn't seem to be doing anything. Also, a "(Not Responding)" label is displayed in the title bar and the mouse cursor becomes a spinning wheel when it's over the Firefox window.Also, the mouse becomes a spinning wait cursor when it's over the Firefox window. This article gives you solutions to Firefox hangs depending on when they happen.

• If Firefox does not start at all, see Firefox won't start - find solutions.
• If Firefox uses a lot of computer resources, see Firefox uses too much memory or CPU resources - How to fix.
• If you get an "unresponsive script" warning, see Warning Unresponsive script - What it means and how to fix it.
• If Firefox closes unexpectedly, see Troubleshoot Firefox crashes (closing or quitting unexpectedly).

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

Firefox hangs at random times

If Firefox seems to hang randomly and not after a specific action (for example, downloading a file or quitting Firefox), try the solutions in this section.

Create a new places database

If hangs are periodic, it may be caused by a corrupted places database.

To create a new places database, do the following:

1. Open your profile folder:

   • Click the menu button , click Help and select More Troubleshooting Information.From the Help menu, select More Troubleshooting Information. The Troubleshooting Information tab will open.
   • Under the Application Basics section next to Profile FolderProfile Directory, click Open FolderShow in FinderOpen Directory. A window will open that contains your profile folder.Your profile folder will open.Your profile directory will open.
   Note: If Firefox displays an error after clicking Open Folder or if you are unable to open or use Firefox, follow the instructions in Finding your profile without opening Firefox.

2. Click the Firefox menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu and select Quit. Wait until Firefox has completely quit.
3. In the Firefox profile folder, find and rename the files places.sqlite to places.sqlite.old and places.sqlite-journal to places.sqlite-journal.old (if it exists).
   • To rename a file, right-click on it and select rename from the menuclick on it once to select it and then click a second time on the file name to make it editable. Then add .old to the end of its name.
4. Finally, reopen Firefox.
   • When Firefox reopens it will create a new places database. Your browsing history will be lost but Firefox will automatically import your bookmarks from the most recent backup file.

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. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the General panel.
3. Under Performance, uncheck Use recommended performance settings.
   Additional settings will be displayed.

   

4. Uncheck Use hardware acceleration when available.
5. Click the Firefox menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu and select Quit.
6. 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.

Change the PAC implementation

If you're using a proxy auto-config 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. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. In the General panel, go down to the Network Settings section.
3. Click Settings…. The Connection Settings dialog appears.
4. 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 workaround to your network administrator.
5. Click Cancel.

Firefox hangs after using it for a long time

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.

Firefox hangs when 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. Open the Library window using one of these methods:
   • Click the Downloads button on the toolbar, if it's available, and click Downloads from the menu.
   • Click the menu button and click Downloads from the menu.
2. Click the Clear Downloads button at the top of the Library window.
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 (such as a shared volume or USB drive) is no longer available. To fix this:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the General panel.
3. Under Downloads, select Save files to and click the ChooseBrowse button.
4. In the Choose Download Folder window, choose a new folder location.
5. Close the Settings 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.

Firefox hangs when you quit it

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 an error message, Firefox is already running, but is not responding.A copy of Firefox is already open. 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 - How to fix for other causes and solutions).

Based on information from Firefox hangs (mozillaZine KB)