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Troubleshoot Firefox issues using Safe Mode

Safe Mode is a special Firefox mode that can be used to troubleshoot and fix problems. Safe Mode temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes) that might be causing problems. By comparing Firefox behavior in normal mode to its behavior in Safe Mode you may be able to pinpoint the cause of the problem.

Note: Windows users may be familiar with a Safe Mode for Windows. Firefox Safe Mode has no connection to Windows Safe Mode.
The Refresh Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Consider using it before going through a lengthy troubleshooting process.

How to start Firefox in Safe Mode

Click the menu button New Fx Menu , click help Help-29 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

SafeMode-Fx35

You now have two options:

  • Clicking the Start in Safe Mode button will temporarily disable your extensions and themes, turn off hardware acceleration and reset toolbar and button customizations. When you leave Safe Mode and start Firefox up normally, your extensions, themes, and 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. See Refresh Firefox - reset add-ons and settings for more information about this option.

Troubleshooting problems in Safe Mode

Once Firefox is 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 could be plugins or changes made to Firefox preference settings, which are not disabled in Safe Mode. See the following articles for solution:

The problem does not happen in Safe Mode

If the problem does not happen in Safe Mode, it is most likely because of an extension, theme or hardware acceleration.

Exiting Safe Mode

  1. Click the menu button New Fx Menu and then click ExitQuit Close 29 .
  2. Start Firefox as you normally would.




Based on information from Safe mode (mozillaZine KB)

Customize this article

Firefox

Firefox for Android

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Firefox OS

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Version History
Revision #:
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Last update:
3 weeks ago
Updated by:
 
Comments

See /forums/knowledge-base-articles/530789 for related discussion about this article. For discussion about the Template:safemode used in this article, see /forums/knowledge-base-articles/704931.

I removed the fx3 content and the fx35&fx4 tags, replaced a note by a warning, changed keywords. It needs review.

mverdi approved it.

Hi,

Shouldn't the part about Disabling add-ons in the Safe Mode Window have a note saying it's not permanent (you can just re-enable them)?

Jack

I agree. In fact, the warning should be changed to say that some of these changes cannot be undone, along the lines of:
http://kb.mozillazine.org/Safe_Mode#Safe_Mode_options (Quote:)

When you select any of these options and click the "Make changes and restart" button, Firefox <snip> will restart in normal mode with the selected changes. Warning: These changes will remain in effect in subsequent browser sessions. Some of these changes cannot be reversed.
  • Disable all add-ons - Disables all themes and extensions; starting in Firefox 3.5, this option also disables all installed plugins. You can use "Tools -> Add-ons" to selectively re-enable them when you restart Firefox <snip>.
  • Reset toolbars and controls <snip> - Removes any Toolbar customizations you may have made via the "Customize Toolbar" dialog. Also restores default window size/position and tree sort order and resolves various localstore corruption issues. Warning: Unless you made a backup copy of "localstore.rdf", this change cannot be reversed without re-customizing your toolbars.
  • Delete all bookmarks except for backups <snip> - Replaces your bookmarks with the default set of bookmarks (your browsing history is left intact). If you select this option and want to undo the change, you will need to restore your bookmarks from backup.
  • Reset all user preferences to (Firefox <snip>) defaults - Resets any user-set preferences to the default values (except for those set in the optional "user.js" file) and restores the default theme. Warning: This change cannot be reversed unless you made a backup copy of the "prefs.js" file. Does not affect any "userChrome.css" or "userContent.css" changes.
  • Restore default search engines - Adds back all of the default search engines included with your version of Firefox <snip> if some are missing. It does not remove any added search engines and you can later remove any unwanted search engines that were added back.

Yes, that's much better for anyone non-technical. But maybe the part about the Bookmark backups should be a bit clearer, i.e. :

If you've saved any bookmarks after the last backup, restoring the defaults will erase those changes, so it's advisable to make a manual backup before using this option (link to: "Backing up and restoring bookmarks").

I made a revision to the article based on the above. It needs review.

(Bump) I made revisions to the article on Nov 23 that are still waiting for review.

(For the record)

Revision id: 18777
Created: Nov 23, 2011 10:54:54 AM
Creator: AliceWyman
Reviewed: Yes
Ready for localization: Yes
Reviewed: Dec 22, 2011 2:51:22 PM
Reviewed by: Verdi
Is approved? Yes
Is current revision? Yes
SkipRinPerth

I am assuming "restore default engines" wipes ALL you entries and restores default engines. So I added that statement . Either way a statement needs to let you know what behavior is.

SkipRinPerth said

I am assuming "restore default engines" wipes ALL you entries and restores default engines. So I added that statement . Either way a statement needs to let you know what behavior is.

No, it only restores any default engines that you removed. It does not remove any added search engines. I'll add that to the article.

See Bug 732303 - Redesign safe mode dialog with the profile reset option and comment 26

Looks like the redesign will remove all of the Safe Mode checkboxes and simply offer the options to continue in Safe Mode or Reset Firefox:

Matthew N. [:MattN] 2012-05-29 01:08:04 PDT
(In reply to magnumarchonbasileus from comment #25)
> As a developer i find it very useful & also so do my helpers
> please don't remove it add it with "Start in safe mode" "Reset profile"

Could you give more details on which of the options you found useful and what problems you were trying to solve with them. I was told by people on the SUMO (support.mozilla.com) team that they don't direct users to use the checkboxes. They were removed in this bug because the dialog was confusing with the two different continue buttons and most of the items could be solved just as easily by deleting files from the profile (we now have a button to open the profile folder from about:support):
  • Disable all add-ons
    • Start in safe mode (disables extensions) and then disable the plugins from the add-ons manager
  • Reset toolbars and controls
    • Delete localstore.rdf from the profile
  • Delete all bookmarks except for backups
    • set browser.bookmarks.restore_default_bookmarks to true (before startup or from about:config then restart)
  • Reset all user preferences
    • Delete prefs.js (and the "preferences" directory if it exists) from the profile
  • Restore default search engines
    • Delete search* from the profile
If there was an option which commonly solved users' problems and is better than resetting Firefox then we can consider a way to address that. Could you file bugs (blocking this one) which you have strong arguments for? Otherwise we can discuss this more on the newsgroup at https://www.mozilla.org/about/forums/#dev-apps-firefox

Note: Changes to toolbars and window sizes are not saved ("Reset toolbars and controls" option) and Reset Firefox preferences to troubleshoot and fix problems ("Reset all user preferences to Firefox defaults" option) both instruct users to use the Safe Mode checkboxes. These and possibly other KB articles will need to be changed to explain how to open the profile folder, close Firefox and then delete the related file. Not sure which other KB articles may need updating.

The regular safe mode dialog is not changing - that bug refers only to the special "forced safe mode" that you end up in after multiple startup crashes. If you enter safe mode from the menu or by holding the shift key on startup you will see the regular safe mode menu.

Are you sure about that? Under Attachments (in the bug report) it has

You are right - I totally got that wrong.

How similar/different are the "Restore" options in the UI to the ones in the Safe Mode dialog?

Safe Mode dialog: Reset toolbars and controls vs.
Customize dialog: Restore Default Set

I think in some cases you might still need to zap localstore.rdf because the errant settings are not the ones fixed by Restore Default Set. (The file has a lot of other settings in it.)

Safe Mode dialog: Restore default search engines vs.
Manage Search Engines dialog: Restore Defaults

jscher2000 said

How similar/different are the "Restore" options in the UI to the ones in the Safe Mode dialog?

Safe Mode dialog: Reset toolbars and controls vs.
Customize dialog: Restore Default Set

I think in some cases you might still need to zap localstore.rdf because the errant settings are not the ones fixed by Restore Default Set. (The file has a lot of other settings in it.)

The localstore.rdf reset came up at MozillaZine. I'll quote what I wrote in http://kb.mozillazine.org/Talk:Corrupt_localstore.rdf


Customize Toolbar - Restore Default Set

I removed the newly-added "Firefox 3 - Method" section 1 that described using "View -> Toolbars -> Customize -> Restore Default Set" (which was also available in Firefox 2) as a solution for a corrupt localstore.rdf file. Localstore.rdf stores a lot of other information besides which toolbar items are used (e.g., window size, position and sort order for download actions, bookmarks/places and other persistent window states), which can be seen by viewing the file contents in Notepad. Although "Restore Default Set" restores the default toolbar items, it doesn't restore the default content of the localstore.rdf file as the Safe Mode and manual deletion methods do, which can be verified by using all three methods and comparing the file size and content for each method. The Safe Mode method replaced my 19.9 KB localstore.rdf file with a new file that was less than 1kb, same as manually deleting the 19.9 KB localstore.rdf file. Using "View -> Toolbars -> Customize -> Restore Default Set" only reduced the 19.9 KB localstore.rdf file size by a few bytes. In other words, content that could be corrupt still remained, so it would not be a solution for a corrupt localstore.rdf file. [[User:Alice Wyman|Alice]] 18:29, 31 July 2008 (UTC)


So, deleting localstore.rdf is what the Troubleshoot Firefox issues using Safe Mode option does ... but that's not the same as using the "Restore Default Set" option in the customize toolbar window. If you want to check again, please do, my testing was done quite awhile ago!

Safe Mode dialog: Restore default search engines vs.
Manage Search Engines dialog: Restore Defaults

I don't know ... if all you want to do is add back any missing "default" search engines, I would think that the Use the Search bar in Firefox method should be enough - see http://kb.mozillazine.org/Search_Bar#Restoring_default_search_engines

By the way, comment 26 from the bug report says to Delete search* from the profile as an alternative to the Troubleshoot Firefox issues using Safe Mode" Restore default search engines" option.. So, that would mean deleting search.sqlite and search.json? You should NOT delete the searchplugins folder containing added search engines (if it exists) since the Safe Mode option only adds back missing search engines ... it doesn't remove added ones. I tested that awhile ago (see http://kb.mozillazine.org/Talk:Safe_Mode#Restore_default_search_engines and this discussion). Maybe Michael Verdi or someone else can answer ... or do you want to test?

This is already all done so it is too late to comment with expectation of change. (I asked a question in the contributors forum, /forums/contributors/708499 before Alice pointed out this discussion)

I would have preferred something leaving the easy method of "advanced" changes. Simply leave the options to reset individual settings until later, maybe when they restart after using safemode, rather than as the first options seen.

It is true we often suggest not using the checkbox options on support questions; I think; because

  • it requires more support instructions to change back if the option was not necessary
  • starting in full safemode is the troubleshooting intention and may work to demonstrate a potential solution (then try the appropriate checkbox).

I still think the safe mode reset prefs option was useful, and that the new reset profile option may be overkill in some circumstances.

The Safe Mode window may be missing the "Reset Firefox" option in some cases (e.g., when using a non-default profile). I brought this up in another discussion started by the-edmeister. See this thread for more information and screenshots:

One big thing this article has always failed to do which has been made painfully clear by its new title is that it doesn't explain what to do once you get into safe mode. It only briefly mentions in the into that you need to compare the behavior in safe mode to that of normal mode.

I created new revisions that make this clear by:

  1. New introduction that is a little more clear and is true for all versions of the article.
  2. Added a "Troubleshooting problems in Safe Mode" based on the similar section in Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems
  3. For version <15 I moved the information about making permanent changes to its own section since that is really an extra, separate process that is not troubleshooting.

I'll add this to the Need Changes list. Here's a Windows 7 screenshot:

https://support.mozilla.org/en-US/gallery/image/20517 SafeMode-Fx35

Related bugs:

  • Bug 1027884 - We need a more appropriate name for "Reset Firefox"
  • Bug 1063702 - Update all Reset Firefox strings and relevant UI to reflect improved copy

Related discussion:

I made a new revision to update this article for fx35 I also removed the outdated {for not fx15} content.

underpass

Hello,

One user in the Italian forum had problem with Firefox after having installed Windows 10: the window is completely black, with no menu or option visible.

I suggested to start in safe mode but I didn't remember that this article doesn't show how to start in safe mode with the command

firefox -safe-mode

I think that it's important to restore these instructions.


edit: the user has solved the problem. I think this might turn useful to know, now that many users will probably upgrade to Windows 10.

+ Sounds a good idea to me. The note is still present in Linux versions. Linux does not have the Shift option. (Option option on Macs)

I know we always make easy methods prominent but we still need this method to be documented, although it must be very rare that installing or changing Firefox could affect the Computers Desktop.


Not sure I can see this sort of issue reported recently in en-US

Underpass said

I suggested to start in safe mode but I didn't remember that this article doesn't show how to start in safe mode with the command firefox -safe-mode I think that it's important to restore these instructions.

MozillaZine's article has those instructions. See:

http://kb.mozillazine.org/Safe_Mode#Starting_Safe_Mode