Hello,

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: (Note: Check both folders.)
     • 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.

Please report back to say if this helped you!

Thank you.

Step no.1 says "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." How do I save the setup file to my computer? All I can do after the download is double click on it and then it tries to install/download Firefox. Then I get a box on the screen saying "Firefox must be closed to proceed with this installation. Please close Firefox to continue." Trouble is that according to my laptop PC Firefox is not open, because every time I try to open it, it starts the process with the little blue circle and then nothing.

Try rebooting the computer. Then run the installer.

https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding

https://www.basezap.com/cant-open-firefox-because-a-copy-of-firefox-is-already-open-mac/

https://apple.stackexchange.com/questions/196771/cant-open-firefox-because-a-copy-of-firefox-is-already-open

Hi Fred I did what you said and then rebooted the computer but I still have the same problem - Firefox will not open on my screen. As well, even though I have hit End Process for Firefox on the Task Manager, when I try to start Firefox again, not only does nothing happen but the Task Manager says it is operating. I tried End Task again and cleared Firefox from the Task Manager, and rebooted again but still the same - when I try to open Firefox nothing happens on my screen but the Task Manager says it is there.

Should I just go to the Control Centre and Program Files and just uninstall it, then reboot the PC and install FFox again? But if I do that won't I lose all my bookmarks?

DougFoskett said

Firefox will not open on my screen

Do you mean that Firefox is running, but the window is not showing?

https://support.mozilla.org/en-US/kb/changes-toolbars-and-window-sizes-are-not-saved You may have corrupt xulstore.json file.

Close Firefox. Open your file browser to this hidden location:

• Mac: *~/Library/Application Support/Firefox/Profiles
• Linux: *~/.mozilla/firefox/Profiles
• Windows: %AppData%\Mozilla\Firefox\Profiles
• *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles
• Windows XP: C:\Documents and Settings\<user>\Application Data
  \Mozilla\Firefox\Profiles\

Search for the above files. Then rename or delete them. Restart Firefox.

DougFoskett said

But if I do that won't I lose all my bookmarks?

Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.