If Firefox suddenly misbehaves, reinstalling it or clearing everything can feel like the fastest escape. A more useful first question is: does the same problem happen with extensions and several customizations temporarily switched off? Firefox’s Troubleshoot Mode helps you make that comparison.
Scope: current Firefox desktop on Windows 11, supported macOS, or a supported Linux distribution. Older releases, managed installations and other languages may differ. This is not a Firefox mobile guide. Time: about 10–20 minutes for the initial comparison. Difficulty: beginner.
You need: access to Firefox, a repeatable example of the problem, and any sign-in details needed to revisit the affected page. Save unfinished forms and work before restarting. This guide uses menus, so there are no terminal commands to run.
1. Define one problem you can repeat
Pick a specific action: opening a particular page, starting one video, or using a toolbar button. Write down what you expected and what actually happened. “The video freezes after I press Play” gives you a much stronger comparison than “Firefox feels broken.”
Keep the test small. Use the same page and action after each restart, and avoid installing an update, changing the network and altering several settings during the same comparison. Those changes might help, but they make it harder to explain which one mattered.
For high CPU or memory use, Mozilla recommends reviewing resource-heavy tabs and other applications too. Firefox’s about:processes page can help identify busy tabs and extensions. A quieter browser after closing twenty tabs is a different observation from a browser that improves with the same tabs in Troubleshoot Mode. See Mozilla’s resource-usage guide.
2. Start the temporary diagnostic session
Open Firefox’s menu, choose Help and Report (or Help, depending on the version), then Troubleshoot Mode…. Confirm Restart. In the next dialog, choose Open.
Choose Open, not Refresh Firefox. Troubleshoot Mode temporarily disables extensions, applies the default theme and turns off hardware acceleration, among other changes. Refresh Firefox is a separate operation that changes the profile. Mozilla explains the temporary mode in its Troubleshoot Mode instructions.
Do the exact action you recorded in step 1. For a problem that happens occasionally, allow a comparable amount of time; one successful attempt is a clue rather than proof that you have found a permanent fix.
3. Read the result before changing anything
The problem disappears: something disabled in this session is a useful suspect. That does not identify a specific extension by itself, because the mode changes several things together. Continue with a controlled test in normal mode.
The problem remains: stop treating extensions as the obvious explanation. Troubleshoot Mode does not reset every Firefox preference, and it does not isolate your network, the website or the rest of your computer. Mozilla’s broader diagnostic guide describes further paths.
For example, a page that fails in both sessions and also fails in another browser deserves a different investigation from a page that fails only when one Firefox extension is enabled. Record that distinction instead of repeatedly resetting the browser.
4. Leave Troubleshoot Mode
Quit Firefox completely, then launch it normally. The temporary mode’s changes should be undone. Your extensions and previous settings return to their pre-test state; any changes you make manually afterward are a separate matter.
If Firefox seems stuck in the mode, a window closing may not have ended the entire application. Save your work and restart the computer if necessary, then open Firefox normally. Repeated startup crashes can also bring back a troubleshooting prompt. See Mozilla’s stuck-in-mode guidance.
5. Test one suspect at a time
If the temporary session helped, use Extensions and Themes → Extensions in normal mode. Note which extensions are enabled, switch them off using their toggles, quit and reopen Firefox, then repeat your test. Disable rather than uninstall while you investigate.
If that helps, re-enable extensions individually, restarting and retesting each time. When the problem returns, the most recently restored extension is a strong lead. Turn it off again and repeat the check before blaming it; interactions between extensions are possible.
If extensions make no difference, test the default System theme separately. For display glitches, test hardware acceleration separately: in Settings, find Performance—Mozilla’s current instructions place it under Tabs and browsing. Clear Use recommended performance settings, then Use hardware acceleration when available, and fully restart Firefox. If your layout differs, search Settings for “performance.”
Record the original settings and restore any change that did not help. Hardware acceleration can reduce CPU and memory load, so turning it off is a diagnostic comparison rather than a general speed recommendation. For detailed isolation steps, follow Mozilla’s extensions, themes and acceleration guide.
When this test is not enough
A problem confined to one site may need site-specific investigation. If cookies or stored site data are the next justified step, our guide to clearing cookies for one website keeps that action focused. Clearing site data can sign you out; it is not required just to enter Troubleshoot Mode.
Avoid treating Refresh Firefox as the final button in this exercise. Mozilla says it retains important items such as bookmarks and passwords, but removes extensions and other customizations, including extension data and modified preferences. Read the full refresh consequences before considering it. This guide does not ask you to refresh, delete a profile or reinstall Firefox.
How to confirm you have a useful result
Finish with a simple record: the action you tested, whether it failed in normal mode, whether it failed in Troubleshoot Mode, and the one change that affected it. A repeatable before-and-after result is more useful than a long list of changes you cannot retrace.
It was not executed in a Firefox desktop session for this article, and no performance improvement or fix rate is claimed. BrowserOS was used to inspect the source documentation and published page.
Optional gear
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SteelSeries QcK Edge Medium mouse pad on Amazon (paid link). An optional desk accessory for a mouse. It does not diagnose or repair Firefox problems.
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