Compare the state changes before choosing
| Method | What changes | What the result tells you |
|---|---|---|
| Troubleshoot Mode | Temporarily disables extensions, themes, hardware acceleration and certain other customizations. | A changed result narrows the investigation to disabled features; it does not identify a particular extension. |
| A separate profile | Starts with a separate set of profile data. | A difference suggests profile-related conditions matter; it does not reveal which one. |
| Refresh | Keeps specified data but removes or resets add-ons, permissions and customizations. | A working result does not say which removed setting was responsible. |
Use Troubleshoot Mode · Create or switch Firefox profiles · Refresh Firefox
Begin with a question a temporary test can answer
Record one repeatable action and the result before changing anything. For example: “The same page fails to play a video in this profile.” Test that action in Troubleshoot Mode using Mozilla’s instructions. Select Open for its temporary session; Refresh is a different, permanent action. Exit and restart normally to leave Troubleshoot Mode. Use Troubleshoot Mode
If the problem remains, remember that Troubleshoot Mode does not reset every preference. If it disappears, investigate the disabled features individually. Neither outcome alone proves that the most recent Firefox update caused the problem.
What changes, and what the result tells you
| Method | Documented state change | What our experiment established | Interpretation / recovery |
|---|---|---|---|
| Normal restart | Reopens the same selected profile. | No restart-control comparison was performed. | Record this baseline before comparing a special mode. |
| Troubleshoot Mode | Temporarily disables several features; it does not reset every preference. | The ordinary restart workflow was not tested. | A change narrows the disabled-feature group. Exit and reopen normally. |
| Separate profile | Uses separate profile state. | The injected preference case worked in a clean profile. | The difference does not identify a cause by itself. Keep and return to the original. |
| Refresh | Creates a new profile and resets/removes documented customizations while retaining listed personal data. | The ordinary Refresh workflow was not tested. | Review data and accessibility requirements first; retain the recovery source. |
Run the temporary-mode check and return to normal
- Write down one repeatable action and its failure.
- Choose Troubleshoot Mode from Firefox’s Help menu and allow its restart.
- In the startup dialog, choose Open for the temporary mode. Refresh is the permanent-reset choice.
- Repeat the same action, record the result, then exit and start Firefox normally.
If the behavior changed, test the disabled features individually before naming a cause. If it did not, a preference that this mode leaves in place remains a possible condition. This launch sequence is documentation-checked.
A new profile is a separate comparison
Mozilla documents creating and launching profiles from about:profiles. Keep the original profile. Be aware that creating one can change the default for future launches. Create or switch Firefox profiles
For an illustrative clean comparison, use harmless test data and avoid immediately bringing your usual extensions and synchronized settings into it: that would change the conditions you intended to compare. This is an experiment design, not a claim that a clean profile fixes all failures.
Make a separate-profile comparison
- Open
about:profilesand identify the current profile. - Create a separately named test profile and launch it in another browser window.
- Repeat a harmless version of the same action before adding your usual extensions or synchronized state.
- Record the difference and return to the original profile when done; avoid deleting it as part of diagnosis.
Create or switch Firefox profiles
A result difference narrows the conditions to investigate. In our controlled example, one changed JavaScript preference explained a failed button. The clean profile worked, but that result alone did not identify the preference; we knew it because we had deliberately set it.
Understand Refresh before making a permanent change
Mozilla lists bookmarks, history and passwords among the data Refresh retains. Extensions, website permissions and changed preferences are among the state it removes or resets. Accessibility customizations may need to be recreated. Availability also depends on the profile system and Firefox version. Refresh Firefox
If a permanent Refresh is an informed choice
Review the preservation/removal table above and your recovery copy first. Save accessibility customizations and settings you would need to recreate.
- Open Firefox’s troubleshooting-information page.
- If Refresh is available for this profile/version, read and confirm its permanent-change prompt.
- After Firefox restarts, review its imported-data summary and check the personal data you needed to preserve.
- Reconfigure only the required customizations and retest the original symptom. Keep the old-data folder until recovery is complete.
These steps are based on current documentation. The experiments did not exercise Refresh or certify that every item survives it. If the control is unavailable, follow the source’s version/profile qualification instead of forcing a reset by deleting files.
Use the outcome to choose the next investigation
Write down what changed and which result repeated. A one-site problem belongs in the website guide; missing bookmarks belong in the data guide. For an unresolved reproducible failure, a concise support report with version, symptom and test results is more useful than an untested claim about the cause.
What our controlled Firefox test showed
A harmless button failed in a profile where JavaScript had deliberately been disabled, worked in a clean profile, and worked again after that one preference was reversed. This tests the interpretation of a clean-profile difference; it does not reproduce a Firefox regression or test a Refresh restart.
Automated checks on Windows with the Playwright-patched Firefox 155.0 engine and Mozilla geckodriver. Fresh profiles and fake data only.
The test notes record the method and results. Bookmark export/import used Firefox’s core APIs; menu instructions are documentation-checked. Built-in Backup, Sync accounts, Refresh and safe-mode restarts were outside the experiments.
Sources & scope
Source checks are dated individually below. Interface labels and availability may vary by version and platform. Controlled Windows Firefox experiments are described in this guide and in the linked test notes.
- Use Troubleshoot Mode Temporary changes and interpreting results · Checked 2026-10-08
- Create or switch Firefox profiles Manage profiles when Firefox is open · Checked 2026-10-07
- Refresh Firefox What Refresh preserves and removes · Checked 2026-10-08
Source review: Firefox Updates Verification Desk, an automated editorial role. Read the AI and verification disclosure.