Safe Mode

This article applies to Firefox and Thunderbird.

Safe Mode is a debugging startup mode where all the extensions you have installed are disabled and the default theme is used. Note however that all available plugins are used. 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)" or "Mozilla Thunderbird (Safe Mode) aka (No Extensions)" shortcut in the Mozilla Firefox or Mozilla Thunderbird program folder on the Windows Start Menu. If you have deleted this shortcut, you can start Firefox or Thunderbird in Safe Mode by going to "Start -> Run" and entering (using Firefox as an example):

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

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

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 listed in the Extensions Manager will be grayed out. You will still be able to select them, but only for the purpose of upgrading or uninstalling (the options button will be disabled).

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.
• 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

• Reset toolbars and controls - removes all toolbar customizations, does not reset your theme to the default theme
• Reset bookmarks to Firefox defaults - Use with caution, as selecting this option replaces your current bookmarks with the default set of Firefox bookmarks. [3]
• Reset all user preferences to Firefox defaults - this resets your Options and other preference settings to the default values (except for those set via the user.js file) and resets the theme to the default.

These additional options are available starting in Firefox 2:

• Disable All Add-ons - this disables all your extensions and themes and resets your theme to the default theme. This means that Firefox will start as if you have no extensions or themes installed. You will need to manual "enable" each one again by opening the add-on manager, highlighting the extension/theme and pressing the "enable" icon. This allows you to enable your add-ons one at a time, until you find the one that is causing the problem.
• Reset Default Search Engines

Buttons

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