How to start Firefox in Troubleshoot ModeSafe Mode

Click the menu button , click Help, select Troubleshoot Mode… and click Restart in the Restart Firefox in Troubleshoot Mode? dialog.

Note: You can also start Firefox in Troubleshoot Mode by holding down the shift key while starting Firefox.holding down the option key while starting Firefox.quitting Firefox and then going to your Terminal and running: firefox -safe-mode
You may need to specify the Firefox installation path (e.g. /usr/lib/firefox)

Click the menu button , click Help, select Restart With Add-ons Disabled… and click Restart in the Restart With Add-ons Disabled dialog.

Note: You can also start Firefox in Safe Mode by holding down the shift key while starting Firefox.holding down the option key while starting Firefox.quitting Firefox and then going to your Terminal and running: firefox -safe-mode
You may need to specify the Firefox installation path (e.g. /usr/lib/firefox)

Troubleshoot ModeSafe Mode window

You will have two options:

• Clicking the Start in Safe ModeOpen 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 ModeSafe Mode and start Firefox normally, your add-ons and other settings will return to the state they were in before you entered Troubleshoot ModeSafe Mode.
• Clicking the Refresh Firefox 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 ModeSafe Mode

After you start Firefox in Troubleshoot ModeSafe Mode, you'll want to test its behavior and see if the problem goes away.

The problem happens in Troubleshoot ModeSafe Mode

If the problem still happens in Troubleshoot ModeSafe 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 ModeSafe 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 ModeSafe Mode

If the problem does not happen in Troubleshoot ModeSafe Mode, the most likely cause is an extension, theme or hardware acceleration. See this article for solutions:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Exiting Troubleshoot ModeSafe Mode

1. Click the Firefox menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu and select Quit.
2. Start Firefox as you normally would.
   • If Firefox keeps starting in Troubleshoot ModeSafe Mode, see Firefox is stuck in Troubleshoot Mode.

More information (Advanced users)

In addition to disabling add-ons (extensions and themes) and turning off hardware acceleration, Firefox Troubleshoot ModeSafe Mode disables Enhanced Tracking Protection and Safe Browsing features. Firefox Troubleshoot ModeSafe Mode also disables the JavaScript Just-in-time (JIT) compiler and ignores the optional userContent.css and userChrome.css files (if present). The xulstore.json file, which saves customizations to window sizes, toolbar settings and controls, is also ignored; however, any changes stored in modified preferences remain in effect.

Based on information from Safe mode (mozillaZine KB)