From MozillaZine Knowledge Base

This article applies to Firefox and Thunderbird.
Note: SeaMonkey 2 (not yet released) can also be started in Safe Mode.

Safe Mode is a debugging startup mode where all added extensions are disabled and the default theme and toolbar settings are used. Note, however, that all available plugins are used and any changes made to options and preferences remain in effect. In Firefox, Safe Mode includes troubleshooting options such as the ability to reset toolbars, bookmarks and preferences. [1]

Starting Safe Mode

To enter Safe Mode you must first make sure Firefox or Thunderbird is not running in the background. This includes all windows like the Download Manager and Extensions that open in a separate window.

Windows

This should not be confused with restarting the computer in Windows Safe Mode!

Use the "Mozilla Firefox (Safe Mode)", "Mozilla Thunderbird (Safe Mode)", or "Mozilla Thunderbird (No Extensions)" shortcut in the Mozilla Firefox or Mozilla Thunderbird program folder on the Windows Start Menu. If this shortcut is missing, you can start in Safe Mode by selecting "Start -> Run" (on Windows Vista, use "Start Search" or enable the Run box, as described here) and entering,

For Firefox, one of these:

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

For Thunderbird, one of these:

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

Adjust the path accordingly, if you installed your Mozilla program in a different location than shown above.

Linux

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

• /path/to/firefox/firefox -safe-mode

Mac OS X

On Mac OS X, go to Utilities (in the Applications folder) and open Terminal, then run (for Firefox):

• /Applications/Firefox.app/Contents/MacOS/firefox -safe-mode

And for Thunderbird, this is the line to run in Terminal:

• /Applications/Thunderbird.app/Contents/MacOS/thunderbird-bin -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're in Safe Mode

Thunderbird

• 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.
• Thunderbird will be using the default theme.

Firefox

• 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 [2].

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.

• Disable all add-ons - Disables all added themes and extensions. You can use the "Add-ons" tool 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.
• Reset bookmarks to Firefox defaults - Replaces your bookmarks with the default set of bookmarks. Caution: If you select this option and want to undo the change you 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, Amazon.com, Answers.com, Creative Commons, eBay, and in Firefox 3, Wikipedia) if some are missing. It does not remove any added search engines.

Buttons

• 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

• Standard diagnostic - Firefox
• Standard diagnostic - Thunderbird

External links

• Safe Mode (Firefox Support)