Safe Mode

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Safe Mode is a debugging startup mode available in Firefox, Thunderbird, and 模板:SeaMonkey 2, where all added extensions are disabled, the default theme is used, and default localstore settings (toolbar settings and controls) are used. Starting in Firefox 3.5, the new Just-in-time (JIT) JavaScript compiler is also disabled. Starting in Firefox 3.6, any changes made via userContent.css and userChrome.css are disabled in Safe Mode. In Firefox 4, hardware acceleration is also disabled. Any changes made to preference settings are unaffected and all available plugins are used in Safe Mode.

In Firefox, Safe Mode includes a number of troubleshooting options that allow you to make changes upon browser restart, such as disabling all add-ons or resetting preferences. (see below).

Starting Safe Mode

All systems

  • Starting with Firefox 4 and Thunderbird 3.3, you can restart in Safe Mode via "Help -> Restart with Add-ons disabled...". When it restarts, a Safe Mode options window will appear (see below). [1]

To enter Safe Mode in other Mozilla applications (or, in Firefox 4, if you can't open Firefox or use the Help menu) you must first make sure Firefox/Thunderbird/SeaMonkey is not running in the background (including all windows like the Download Manager that open in a separate window) before following the instructions given below.


Use one of these methods to start your Mozilla application in Safe Mode. This should not be confused with restarting the computer in Windows Safe Mode!

  • Starting in Firefox 4: Hold down the Shift key while double-clicking the Firefox icon. (If the Profile Manager opens, select a profile and then hold down the Shift key again while clicking the "Start Firefox" button.) [2] [3]
  • In other Mozilla applications, use the "Mozilla Firefox (Safe Mode)", "SeaMonkey (Safe Mode)", "Mozilla Thunderbird (Safe Mode)", or "Mozilla Thunderbird (No Extensions)" shortcut in the Mozilla Firefox, SeaMonkey, or Mozilla Thunderbird program folder on the Windows Start Menu. Note: The "Mozilla Firefox (Safe Mode)" shortcut has been removed in Firefox 4.

As an alternative method, select "Start -> Run" (on Windows 7/Vista, enable the Run box, as described here) and enter the following in the Windows Run box:

For Firefox, one of these:

  • firefox -safe-mode
  • "C:\Program Files\Mozilla Firefox\firefox.exe" -safe-mode
  • "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -safe-mode

For Thunderbird, one of these:

  • thunderbird -safe-mode
  • "C:\Program Files\Mozilla Thunderbird\thunderbird.exe" -safe-mode
  • "C:\Program Files (x86)\Mozilla Thunderbird\thunderbird.exe" -safe-mode

For SeaMonkey, one of these:

  • seamonkey -safe-mode
  • "C:\Program Files\SeaMonkey\seamonkey.exe" -safe-mode
  • "C:\Program Files (x86)\SeaMonkey\seamonkey.exe" -safe-mode

Adjust the path accordingly based on the actual installation directory (e.g., on 64-bit Windows, use "Program Files (x86)" instead of "Program Files") or if you installed your Mozilla program in a different location than shown above.


On Linux, you can go to your Terminal and run (for Firefox):

  • /path/to/firefox/firefox -safe-mode

Mac OS X

Hold down the Option key while starting your Mozilla application. (If the Profile Manager opens, select a profile and then hold down the Option key again while clicking the button to start Firefox, Thunderbird, or SeaMonkey.) [4]

As an alternate method, go to Utilities (in the Applications folder) and open Terminal, then run:

For Firefox:

  • /Applications/ -safe-mode

For Thunderbird:

  • /Applications/ -safe-mode

For SeaMonkey:

  • /Applications/ -safe-mode

If you have installed the application to another location, modify the path as such. It's the "-safe-mode" command line parameter that's crucial here.

How to know you are in Safe Mode

Thunderbird and SeaMonkey 2

  • All extensions will be disabled. You will still be able to select them in the Add-ons/Extensions list but only for the purpose of upgrading or uninstalling (the options button will be disabled).
  • Default toolbar settings and controls will be used.
  • The default theme will be used.


  • A window called Firefox Safe Mode with some troubleshooting options appears.

At that point, you can either continue to Safe Mode or select some troubleshooting options and restart Firefox in normal mode to apply the changes.

If you choose to continue in Safe Mode:

  • All extensions will be disabled (but this will not reset any Firefox preferences that some extensions may modify).
  • Firefox will be using the default theme.
  • Default toolbar settings and controls will be used [5].

If you choose any of the troubleshooting options, the changes are only applied if you choose Make Changes and Restart.

Safe Mode options in Firefox

When you select any of these options and choose the "Make changes and restart" button, Firefox will restart in normal mode and the selected changes will be made. [6]


  • Disable all add-ons - Disables all themes and extensions; starting in Firefox 3.5, this option also disables all installed plugins. [7] You can use "Tools -> Add-ons" to selectively re-enable them when you restart Firefox (details here).
  • Reset toolbars and controls - Removes any toolbar customizations you may have made via the "Customize Toolbar" dialog. Also restores default window size/position and tree sort order and resolves various localstore corruption issues.
  • Delete all bookmarks except for backups (Firefox 3.6 and above [8]) or Reset bookmarks to Firefox defaults (Firefox 3.5 and below) - Replaces your bookmarks with Firefox defaults (your browsing history is left intact). Caution: If you select this option and want to undo the change will need to restore your bookmarks from backup.
  • Reset all user preferences to Firefox defaults: - Resets any user-set preferences to the default values (except for those set in the optional user.js file) and restores the default theme. Does not affect any userChrome.css or userContent.css changes.
  • Restore default search engines - Adds back all of the default search engines (currently Google, Yahoo,,, Creative Commons, eBay, and in Firefox 3, Wikipedia) if some are missing. It does not remove any added search engines.


  • Make Changes and Restart - This restarts Firefox in normal mode and applies the changes in any of the options selected above.
  • Continue in Safe Mode - Starts Firefox in Safe Mode (this will not apply any of the options selected above).
  • Exit

See also

External links

Related bug reports