It sounds like you or the install/uninstall software has messed up the Firefox program files and folders.

The good news is that the most important information is actually in the Firefox profile. That is in a separate location. The profile stores your data and settings.

• See Profiles - Where Firefox stores your bookmarks, passwords and other user data

If you wish to play safe then as a belts and braces method backup the Firefox profile before you do the reinstall. Try if possible to open the profile from with-n Firefox, and check that is your correct profile - just in case that is also duplicated. When you use Firefox do you see the correct and expected set of bookmarks for instance.

• Back up and restore information in Firefox profiles

Do a clean install, involving deleting the program files. I explain the full procedure lower down in this post.

Note it is not normally a good idea to use third party uninstallers on Firefox, or to use third party cleaning utilities on Firefox's files.

Please post back to say how you get on.

Clean ReInstall

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

To do a clean reinstall of Firefox, please follow these steps: Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

Thank you, John99. I'll try that and let you know.

So a "clean reinstall" is not clean after all, since it keeps the profile ? And it's less clean than a "refresh", since the refresh wipes out extensions and settings ? How strange...

I will explain later. Tried on a phone but lost the post H battery is nearly flat.

Clean install is our jargon. That type of install deals with issues where the core program files could have been corrupted.

Ordinary installs and uninstalls leave some settings and data behind. That is quite common with applications and allows reinstalling whether immediately or at later date without the end user needing to be explicitly aware of what would have needed to be backed up and saved.

The Refresh, previously known as a Reset, copies the profile as a backup, then clears some of it including the Firefox extensions. It does try to retain important things like passwords and bookmarks. Its big advantage is it is use friendly and can be offered from a click here button. It would be nice if at some future date we could also backup the extensions and allow them to be restored one at a time if necessary, but it turns out that's rather complex and I'm not sure if the idea is still being worked on.

There are better troubleshooting methods and potential fixes that are nearly as easy. For instance it is fairly easy to create a new test profile, but we are not offering that as a one click solution, and for historic reasons Firefox (Mozilla) is trying avoid supporting use of multiple profiles (although we now do that intentionally with Developer Edition).

Hi again John99, and thanks for all the detailed info.

I have now uninstalled / reinstalled per your instructions and it's working, however something strange happened so I still need your help. Let me describe what I did.

• Made multiple backups of profile + bookmarks + settings + extensions through various means (Firefox export, manual copy, FEBE, disk imaging), so I'm all set.

• Deleted install folder.

• Downloaded FF 45 from all-languages page.

• Installed with monitoring by Revo Uninstaller Pro.

• Despite checking the relevant box in the install wizard, no shortcut was created on the Desktop.

• FF launches. UI customization seems back in place. Bookmarks are there, but it's an old set. Some extensions are installed, but not all.

• Closed FF (I think).

• Tried to launch FF through my previous Taskbar shortcut.

• Maybe FF launches (not sure I remember correctly).

• Dialog box opens with error message : Update failed, the partial update failed, Firefox will try again by downloading a complete update (could it be a leftover from my previous update attempt ?).

• I don't click OK, and close the box through x.

• Went in the install folder, created a shortcut manually, pinned to the taskbar, launched FF.

• This time, all my extensions are there, and the newest set of bookmarks as well ! FF seems more reactive than before.

• First time I successfully used the shortcut in the Taskbar, another icon appeared in the Taskbar. So I pinned the latter and deleted the former. Now I only have one icon.

I'm afraid some old bits of FF might be lurking somewhere and come back to bite me. Any thoughts ?

Note : I have two Windows user accounts, one admin, one non-admin, and FF is installed for both. Under each Windows user account I have two FF profiles, the one I actually use and another for reference only, which stays in a virgin state, like it was straight out of install.

I have Profile Manager set to open each time I launch FF to offer both profiles, but I always choose the same. I mostly work out of my non-admin Windows user account. I installed FF under non-admin.

If you desire you may use Firefox Sync to make all Synced Firefoxes similar.

• How do I set up Sync on my computer?
• How do I choose what information to sync on Firefox?

If you Sync the bookmarks it will sill be prudent to make regular manual backups of the bookmarks because Sync occasionally corrupts bookmark collections. Personally I avoid using Sync, I have multiple Systems, accounts, Firefox versions, & Fx accounts but after bad experiences with Sync I gave up on it.

If trying to restore or Import bookmarks note that the HTML imports add to the bookmarks collection, but the JSON restores overwrite the current collection. The library exposes the individual restore sets bookmark number, date and size.

• Restore bookmarks from backup or move them to another computer
• Import Bookmarks from an HTML file

The actual database holding the working Bookmarks and History is a file called places.sqlite each profile will have such a file.

• Recovering important data from an old profile_bookmarks-downloads-and-browsing-history

Firefox itself does backup some files or even the profile but never by making a .bak copy of the profile within another profile. I suspect that will be some third party backup or installer utility you use, or by your own attempts to create additional profiles.

The shortcut is created by Firefox by default, but I am sure you make one yourself. In Windows, it will drag from the relevant firefox-exe then be modified by the Profile Manager. You may also be interested in reading

• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox
• http://kb.mozillazine.org/Bypassing_the_Profile_Manager#Desktop_shortcut

Firefox should install ok from ordinary; none Admin; Windows accounts

• What is the Mozilla Maintenance Service?

Generally it is good practice to use multiple accounts and so avoid using admin accounts unnecessarily. It is safer and more secure.

It is possible to make multiple installs of Firefox, but that is normally only done for testing or if multiple versions are installed. This old article explains about cancelling pending updates

• Updates reported when running newest version_delete-update-configuration-files

Personally I would avoid trying to use the same profile for multiple users. Maybe initially clone a profile, or sync it. You discussed this in

• Is it possible to have a single profile for several users ? /questions/1095249

There are special steps that can be taken if you deploy Firefox across multiple machines e.g. on an intranet

• For instance the slightly outdated article https://mike.kaply.com/2012/04/13/customizing-firefox-extensions-and-the-cck-wizard/#more-1541 (Kaply still provides CCK2 free )