Troubleshoot Mode runs Firefox with some features and customizations disabled (see below for details). If you're having a problem in Firefox that does not occur in Troubleshoot Mode, the cause of the problem is one of the disabled items.
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How to start Firefox in Troubleshoot Mode
Click the menu button 
, click , select and click in the Restart Firefox in Troubleshoot Mode? dialog.
firefox -safe-modeYou may need to specify the Firefox installation path (e.g. /usr/lib/firefox).
Troubleshoot Mode window
You will have two options:
- Clicking the button will start Firefox with the default theme, your extensions will be disabled, and some other features and customizations will be turned off. These changes are temporary. When you leave Troubleshoot Mode and start Firefox normally, your add-ons and other settings will return to the state they were in before you entered Troubleshoot Mode.
- Clicking the button will restore Firefox to its factory default state while saving your essential information. These changes are permanent. See Refresh Firefox - reset add-ons and settings for more information, before you choose this option.
Diagnosing problems in Troubleshoot Mode
After you start Firefox in Troubleshoot Mode, you'll want to test its behavior and see if the problem goes away.
The problem happens in Troubleshoot Mode
If the problem still happens in Troubleshoot Mode, it is not being caused by an extension or theme. Other possible causes include changes made to Firefox preference settings, which are not disabled in Troubleshoot Mode. See the following articles for solutions:
- Troubleshoot and diagnose Firefox problems
- Reset Firefox preferences to troubleshoot and fix problems
The problem does not happen in Troubleshoot Mode
If the problem does not happen in Troubleshoot Mode, the most likely cause is an extension, theme or hardware acceleration. See this article for solutions:
Exiting Troubleshoot Mode
- Click the Firefox menu and select .Click the Firefox menu at the top of the screen and select .Click the Firefox menu and select .
- Start Firefox as you normally would.
- If Firefox keeps starting in Troubleshoot Mode, see Firefox is stuck in Troubleshoot Mode.
What does Troubleshoot Mode disable?
- Add-ons (extensions and themes)
- Hardware acceleration
- Window and sidebar size and position settings
- userChrome and userContent customizations
- JavaScript Just-in-time (JIT) compiler
- Add-ons (extensions and themes)
- Hardware acceleration
- Site Isolation
- Window and sidebar size and position settings
- userChrome and userContent customizations
- JavaScript Just-in-time (JIT) compiler
Based on information from Safe mode (mozillaZine KB)
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