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Firefox Standard Diagnostic Steps
http://kb.mozillazine.org/Standard_diagnostic_-_Firefox

Standard diagnostic - Firefox

This article offers a standard set of steps to follow as a last resort if Firefox is no longer working properly. If you have not done so already, try searching for your specific problem before performing these steps. These steps make an effort to preserve user data (bookmarks, passwords, history, settings, etc.). If you aren't concerned with saving your profile data or if you have a current profile backup [ http://kb.mozillazine.org/Profile_backup ], you can save time by just uninstalling Firefox and removing your user profile data [ http://kb.mozillazine.org/Uninstalling_Firefox ], then reinstalling Firefox, instead of following this article.

Standard diagnostic steps

1. Reboot the computer. If the problem persists, continue on.

2. If you can open the program and use the menus, clear the cache ("Tools -> Options [ http://kb.mozillazine.org/Menu_diffe...nux%2C_and_Mac ]-> Privacy -> Cache -> Clear") and any other private data you don't wish to save such as cookies and download history. If the problem persists, continue on.

3. Close Firefox (if open) using "File -> Exit" and make sure it is not running in the background [ http://kb.mozillazine.org/Kill_application ]. Do not skip this step.

4. Firefox 1.5 only: Start Firefox in Safe Mode [ http://kb.mozillazine.org/Safe_Mode ](not Windows Safe Mode). When the "Firefox Safe Mode" window appears, check the boxes "Reset toolbars and controls" and press the button, "Make Changes and Restart". You will lose any toolbar customizations. If the problem persists, perform step 3 again and continue on.

5. If you have extensions or themes,

* Review the list of problematic extensions [ http://kb.mozillazine.org/Problematic_extensions ]to see if your problem is listed. Also make sure you are using the latest version of your extensions ("Tools -> Extensions -> Find Updates") as some may have problems not listed in the aforementioned article. If the problem is not resolved, continue on.

* Start Firefox in Safe Mode [ http://kb.mozillazine.org/Safe_mode ](not Windows Safe Mode). Firefox 1.5: When the "Firefox Safe Mode" window appears, press the button, "Continue in Safe Mode". This will start the program with all extensions disabled and with the default theme. If the problem exists in safe mode, or Firefox doesn't start in safe mode, continue on to the next numbered step. If the problem goes away in safe mode:

Uninstall your most recently installed or updated extension or theme, perform step 3 again, and start Firefox normally. If the problem persists,

Select the default theme in "Tools -> Themes" and uninstall your extensions in "Tools -> Extensions" (although the extensions appear grayed out, you will still be able to uninstall them). Perform step 3 again and start Firefox normally. If the problem persists, continue on.

6. Important: Back up your profile [ http://kb.mozillazine.org/Profile_backup ] before continuing so that your settings and personal data (such as bookmarks and passwords) will not be lost. Then,

Perform step 3 again and delete the file "XUL.mfl" (Windows), "xul.mfasl" (Linux), or "XUL FastLoad File" (Mac OS X) from your profile folder [ http://kb.mozillazine.org/Profile_folder ]or, in Firefox 1.5, from the "profile temp directory" that also stores the cache [1] [ https://bugzilla.mozilla.org/show_bug.cgi?id=291033 ], for example, under %USERPROFILE%\Local Settings\Application Data\Mozilla\Firefox in Windows 2000/XP or under ~/Library/Caches/Firefox in Mac OS X. This file will be regenerated on next startup. If the problem persists, continue on.

Perform step 3 again, then check the properties of the profile folder [ http://kb.mozillazine.org/Profile_folder ] and its file contents. Remove any "read-only" attributes, particularly if you find files with the ".moztmp" extension such as "bookmarks.html.moztmp" [ http://kb.mozillazine.org/Bookmarks.html.moztmp ]"prefs.js.moztmp" or "cookies.txt.moztmp" [2][ https://bugzilla.mozilla.org/show_bug.cgi?id=257288 ]. If the problem persists or if no "read-only" attributes are found, continue on.

Perform step 3 again, then delete (or rename) the files "downloads.rdf" [ http://kb.mozillazine.org/Downloads.rdf ] "history.dat" [ http://kb.mozillazine.org/History.dat ] "mimeTypes.rdf" [ http://kb.mozillazine.org/MimeTypes.rdf ] and "localstore.rdf" [ http://kb.mozillazine.org/Localstore.rdf ] from your profile folder [Profile_folder]. This will remove your download history, browsing history, changes to download actions and any changes you have made to the toolbars (these files can be later restored if removing didn't help). If the problem persists,

Perform step 3 again, then delete (or rename) the files "prefs.js" [ http://kb.mozillazine.org/Pref.js ] and (if present) "user.js" [ http://kb.mozillazine.org/User.js ] as well as the "extensions" folder and the "chrome" folder (if present) from your profile folder [ http://kb.mozillazine.org/Profile_folder ]. You will lose your customized preference settings and all your extensions and themes. If the problem persists,

Perform step 3 again, then create a new profile [ http://kb.mozillazine.org/Profile_manager ]. Your personal data and settings will not be present when Firefox starts, but they are not gone forever. If the problem is resolved, selectively copy back your important profile data [ http://kb.mozillazine.org/Migrating_..._a_new_profile ] to the new profile. If the problem persists, continue on.

7. Do a clean install:

* Download the Firefox installer [ http://www.getfirefox.com/ ] and save it to the desktop or other location, but do not run it.

* Uninstall Firefox [ http://kb.mozillazine.org/Uninstalling_Firefox ]

* Remove the Firefox installation directory [ http://kb.mozillazine.org/Installation_directory ]

* Open your OS temporary directory (Windows 98/ME: Start -> Run -> Type C:\Windows\Temp -> OK; Windows 2000/XP: Start -> Run -> Type %temp% -> OK) and delete all files and folders contained therein.

* Reinstall Firefox [ http://kb.mozillazine.org/Installing_Firefox ] using the installer you downloaded earlier.

Other solutions

If you've tried all of the above steps, including a clean reinstall:

* Scan your system for viruses, spyware or other malware. If nothing is found:
* With Firefox completely closed [ http://kb.mozillazine.org/Kill_application ], open the application folder [ http://kb.mozillazine.org/installation_directory ](by default, C:\Program Files\Mozilla Firefox on Windows) rename firefox.exe to firefox1.exe, then double-click firefox1.exe. If Firefox runs without problems it indicates that some malicious code has targeted Firefox which your antivirus or spyware scanner currently cannot detect. This should be used only as a temporary workaround until the malware can be found and removed.

* It's also possible that a firewall, ad-blocker, web-accelerator, antivirus or other running program is conflicting with Firefox. Try temporarily disabling these other programs one at a time.

* (Windows) Run the error-checking tool Chkdsk [ http://support.microsoft.com/?kbid=315265 ](Windows 2000, XP) or ScanDisk [ http://support.microsoft.com/?kbid=186365 ](Windows 95, 98, ME).

See also

* Browser will not start up: http://bk.mozillazine.org/Browser_will_not_start_up

* Error loading any website: http://kb.mozillazine.org/Error_loading_any_website

* Profile in use: http://kb.mozillazine.org/Profile_in_use

* Firefox hangs: http://kb.mozillazine.org/Firefox_hangs

* Firefox crashes: http://kb.mozillazine.org/Firefox_crashes

* Reducing memory usage (Firefox): http://kb.mozillazine.org/Reducing_m..._%28Firefox%29

* Issues with Firefox: http://kb.mozillazine.org/Issues_with_Firefox

-- Tom