Hello, certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall 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 http://www.mozilla.org and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
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.

Please report back to see if this helped you!

In #3 of your instructions you say: "Delete the Firefox installation folder, which is located in one of these locations, by default:

   Windows:
       C:\Program Files\Mozilla Firefox"
      

In Windows Explorer, I went to C:\Program Files\Mozilla Firefox. There is no installation folder. There is only one file (a text document) that says "install." I tried deleting that and followed the rest of your instructions and ended up with the same results as before. There is a file under Mozilla Firefox that is called "uninstall." If I click on "helper," I get the same message: "Your computer must be restarted to complete a previous upgrade of Firefox. Do you want to reboot now?"

Try to run the Firefox program once as Administrator (right-click: Run as Administrator).

You may have security software that is interfering with the installation if a reboot is required.

I have tried all of the above as Administrator. I tried disabling my antivirus program and the firewall but neither one of these tries helped

hello, the installation folder from #3 in the original reply is referring to the whole "C:\Program Files\Mozilla Firefox" directory, not any subfolder or file in particular. if the directory is still present after uninstalling firefox through the windows control panel, then please remove the whole "C:\Program Files\Mozilla Firefox" folder & try reinstalling firefox afterwards.

I deleted the folder using Windows Explorer and installed the new version. It worked perfectly. I was hesitant to delete the folder without officially uninstalling the program, thinking it would affect other programs that might have common files being used. All other programs seem to work fine. Thanks SOOO much for your help!

Download a fresh Firefox copy and save the file to the desktop.

• Firefox 20.0.x: http://www.mozilla.org/en-US/firefox/all.html

Uninstall your current Firefox version, if possible, to cleanup the Windows registry and settings in security software.

• Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other profile data are stored in the Firefox Profile Folder and won't be affected by an uninstall and (re)install, but make sure that "remove personal data" is NOT selected when you uninstall Firefox.

• Help > Troubleshooting Information > Profile Directory: Show Folder

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup