Troubleshoot Firefox issues using Safe Mode

Safe Mode is a special Firefox mode that can be used to troubleshoot and fix problems. When you start Firefox in Safe Mode, it temporarily disables add-ons (extensions and themes), turns off hardware acceleration and certain other features, and ignores some customizations (see below to learn more). Comparing Firefox's behavior in normal mode to its behavior in Safe Mode may help pinpoint the cause of the problem.

Windows users may be familiar with Safe Mode for Windows. Firefox Safe Mode has no connection to Windows Safe Mode.

How to start Firefox in Safe Mode

Click the menu button Fx57menu, click Help and select Restart with Add-ons Disabled…. Firefox will start up with the Firefox Safe Mode 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)

Safe Mode window


You will have two options:

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

Troubleshooting problems in Safe Mode

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

The problem happens in Safe Mode

If the problem still happens in Safe Mode, it is not being caused by an extension or theme. Other possible causes include the Adobe Flash plugin or changes made to Firefox preference settings, which are not disabled in Safe Mode. See the following articles for solutions:

The problem does not happen in Safe Mode

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

If some websites work properly in Safe Mode but not in normal mode, Firefox's Content blockingEnhanced Tracking Protection feature may be the cause. To turn off this feature for specific websites, see:

Exiting Safe Mode

  1. Click the Firefox menu Fx57Menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu Fx57Menu and select Quit.
  2. Start Firefox as you normally would.

More information (Advanced users)

In addition to disabling add-ons (extensions and themes) and turning off hardware acceleration, Firefox Safe Mode disables Content blockingEnhanced Tracking Protection and Safe Browsing features. Firefox Safe 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)

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