Troubleshoot Mode runs Thunderbird with some features and customizations disabled (see below for details). If you are having a problem in Thunderbird that does not occur in Troubleshoot Mode, then the cause of the problem is one of the disabled items.

Starting Thunderbird in Troubleshoot Mode

1. Request Troubleshoot Mode

If Thunderbird is not running: Hold down the Shift key while starting Thunderbird.Hold down the option key while starting Thunderbird.From Terminal, run this command: thunderbird -safe-mode
You may need to specify the Thunderbird installation path (e.g. /usr/lib/thunderbird).

If Thunderbird is already running: Click ≡ > Help > Troubleshoot Mode and in the Restart in Troubleshoot Mode prompt, choose Restart.

2. In the Thunderbird Troubleshoot Mode dialog, click Continue in Troubleshoot Mode button.

3. Click ≡ > Help and check if you see Turn Troubleshoot Mode Off in the menu, to confirm that Thunderbird is currently running in Troubleshoot Mode.

Turning Troubleshoot Mode off

Click ≡ > Help > Turn Troubleshoot Mode Off to immediately close Thunderbird and restart it in normal mode.

Or you can just exit Thunderbird and start as you normally would.

Diagnosing problems in Troubleshoot Mode

After you start Thunderbird in Troubleshoot Mode, test its behavior to see if the problem goes away.

The problem still happens in Troubleshoot Mode

If the problem still happens in Troubleshoot Mode, it is not being caused by an extension or theme installed in Thunderbird. Possible causes and solutions include:

• Something wrong with your Thunderbird installation: Reinstall Thunderbird from https://www.thunderbird.net/

• Changes made to Thunderbird preference settings not disabled in Troubleshoot Mode

The problem no longer happens in Troubleshoot Mode

If the problem no longer happens in Troubleshoot Mode, the most likely cause is an extension, theme or hardware acceleration. Possible solutions include:

• Progressively disable extensions in the add-ons manager – ≡ > Add-ons and Themes > Extensions – and check if the problem remains. When the problem goes away, the last disabled extension is probably the trouble causer. You can try to update it, disable it, or remove it.
• Set the default theme in the add-ons manager: ≡ > Add-ons and Themes > Themes
• Try turning off hardware acceleration in Thunderbird's settings: ≡ > Settings > General, then uncheck Use hardware acceleration when available.

What does Troubleshoot Mode disable?

• Add-ons (extensions and themes)
• Hardware acceleration
• Window and sidebar size and position settings (described in terms of Firefox)
• userChrome and userContent customizations
• JavaScript Just-in-time (JIT) compiler