Troubleshoot and diagnose Firefox problems

Firefox Firefox Last updated: 49% of users voted this helpful

Most problems with Firefox can be fixed by following the troubleshooting methods described below. Try these steps in order. If one doesn't work, move on to the next one. If you need extra help with any of this, we have a community of volunteers standing by.

1. Restart your computer

Sometimes problems can be fixed by simply restarting your computer and then starting Firefox again.

2. Clear your cookies and cache

Many problems with loading web pages can be resolved by clearing Firefox's cookies and cached Web content. To learn more, see Clear cookies and site data in Firefox and How to clear the Firefox cache.

To clear cookies and cache all at once:

  1. Click the menu button Fx89menuButton to open the menu panel.
  2. Click History and select Clear recent history…
  3. In the Time range to clear: drop-down, select Everything.
  4. Below the drop-down menu, select both Cookies and Cache. Make sure other items you want to keep are not selected.
  5. Click Clear Now.
  1. Click the menu button Fx89menuButton to open the menu panel.
  2. Click History and select Clear recent history…
  3. In the When: drop-down, select Everything.
  4. Below the drop-down menu, select both Cookies and site data and Temporary cached files and pages. Make sure other items you want to keep are not selected.
  5. Click Clear.

Firefox also has a startup cache that stores certain temporary data, to improve startup speed. Clearing the startup cache and then restarting Firefox can resolve various issues with the Firefox user interface (UI). This will not change your profile data or add-ons.

  1. Click the menu button Fx89menuButton, click Help and select More Troubleshooting Information. The Troubleshooting Information page will open.
  2. Under Try clearing the startup cache, click Clear startup cache… and then click Restart.

3. Restart Firefox in Troubleshoot Mode

Firefox Troubleshoot Mode is a diagnostic mode that disables extensions, uses the default theme, turns off hardware acceleration and uses default toolbar settings, among other changes (see this article for details). To start Firefox in Troubleshoot Mode:

  1. Click the menu button Fx89menuButton, click Help, select Troubleshoot Mode… and click Restart in the Restart Firefox in Troubleshoot Mode? dialog.

    Note: You can also start Firefox in Troubleshoot Mode by holding down the Shift key while starting Firefox.holding down the option key while starting Firefox.quitting Firefox and then going to your Terminal and running: firefox -safe-mode
    You may need to specify the Firefox installation path (e.g. /usr/lib/firefox).
  2. In the next Open Firefox in Troubleshoot Mode? dialog, click Open.
  3. Check whether your problem is still happening while in Troubleshoot Mode.
  • If the problem still happens in Troubleshoot Mode, go on to step 4.
  • If the problem does not happen in Troubleshoot Mode, follow these instructions to troubleshoot extensions, themes, and hardware acceleration.

4. Reinstall Firefox

Some Firefox issues can be caused by a problem with one of the Firefox program files. Follow these steps to completely remove and reinstall Firefox. This process will not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

Note: You might want to print these steps or view them in another browser.
  1. Download and save the installer for the latest official version of Firefox from mozilla.org.
  2. Exit Firefox (if open): Click the Firefox menu Fx89menuButton and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu Fx89menuButton and select Quit.
  3. You may want to make a note of the Mozilla Firefox program folder location (right-click the Firefox desktop icon, select Properties from the context menu and click the Shortcut tab) since there may be leftover files and folders after you uninstall Firefox that should be removed for a clean reinstallation.
  4. Uninstall Firefox from your computer.
  5. If the uninstall did not remove all Firefox program files, manually delete the Firefox program folder, found in one of these locations by default:
    • C:\Program Files\Mozilla Firefox
    • C:\Program Files (x86)\Mozilla Firefox
  6. Reinstall Firefox using the installer you downloaded earlier – see How to install Firefox on Windows for instructions.
  1. Download the latest official version of Firefox from mozilla.org.
  2. Quit Firefox: Click the Firefox menu Fx89menuButton and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu Fx89menuButton and select Quit.
  3. Uninstall Firefox from your computer by opening the Applications folder in the Finder and dragging the Firefox application to the Trash.
  4. Reinstall Firefox – see How to download and install Firefox on Mac for instructions.
  1. Download the latest official version of Firefox from mozilla.org.
  2. Quit Firefox: Click the Firefox menu Fx89menuButton and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu Fx89menuButton and select Quit.
  3. Uninstall Firefox – if you installed Firefox with the distro-based package manager, you should use the same way to uninstall it – see Install Firefox on Linux for details. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory to uninstall Firefox.
  4. Reinstall Firefox – see Install Firefox on Linux for instructions.

Now start Firefox and check to see if your problem has been fixed. If it hasn't, continue with the next troubleshooting method.

5. Refresh Firefox

The Refresh Firefox feature can fix many issues by restoring your Firefox profile to its default state while saving your essential information.
If you have many Firefox customizations, you may want to skip this step and create a new Firefox profile instead (see step 6, below) so that your old profile is easily recoverable from the Profile Manager.

Note: When you refresh Firefox, your bookmarks, browsing history, open tabs, windows, passwords, cookies and web form auto-fill information will be saved. However, your extensions and themes will be removed and your preferences will be reset. Learn more.
  1. Click the menu button Fx89menuButton, click Help and select More Troubleshooting Information.
  2. Click Refresh Firefox… then Refresh Firefox in the confirmation window that opens. Firefox will close to refresh itself.
  3. When finished, a window will list your imported information. Click the Finish button. Firefox will open.
  4. Select whether you want Firefox to restore all or some windows and tabs and click the Let's go! button.
Note: There's a Refresh Firefox button in the Firefox Troubleshoot Mode window, if you can't start Firefox normally. You can also do a manual refresh by creating a new profile and transferring your important data to the new profile.

6. Create a new Firefox profile

Sometimes files in your Firefox profile folder that correspond to the essential information that a Firefox Refresh doesn't remove (such as bookmarks and browsing history) may be causing the issue. You can create a new, additional profile which will not contain any of your old Firefox data. See the Profile Manager - Create, remove or switch Firefox profiles article for instructions.

Other solutions

If you've tried all of these troubleshooting methods, and you're still having problems, here are some other solutions you can try:

Check browser internals

The Firefox Task Manager (about:performanceabout:processes page) lets you see whether tabs or extensions are slowing down Firefox. Telemetry Data shared with Mozilla (about:telemetry page) contains detailed data about performance, hardware, usage, and customization. The Troubleshooting Information page (about:support page) includes other about: page links and troubleshooting resources. (For a list of all about: pages, enter about:about in the address bar.)

Check for issues caused by corrupt or incomplete Visual C++ installation

Some issues are caused by a corrupt or incomplete Visual C++ installation that is missing runtime components (Redistributable Packages) required by Firefox, especially VCRUNTIME140_1.dll. This can happen after installing or uninstalling other software on your computer. To reinstall these components, download and run the latest installer for Visual Studio from Microsoft Visual C++ Redistributable latest supported downloads and then reboot the computer.

Check for conflicts with your Internet security software

Some Internet security software (including antivirus, antispyware, and firewall programs) can cause problems with Firefox, including blocking it from opening websites, crashes, and more. Often you can open the program's settings, remove Firefox from its list of allowed or trusted programs, and it will be re-detected and things should start working again. See Configure firewalls so that Firefox can access the Internet.

Check for malware

Malware (short for “malicious software”) can cause problems with Firefox. Periodically, you should scan your system for viruses, spyware, or other malware. For more information, see Troubleshoot Firefox issues caused by malware.



Based on information from Standard diagnostic - Firefox (mozillaZine KB)

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AliceWyman, Chris Ilias, Underpass, Tonnes, Michele Rodaro, Michael Verdi, scoobidiver, Andrew, Swarnava Sengupta, dskmori, Safwan Rahman, Mozinet, user669794, scootergrisen, Joni, Artist, fffknol
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