Now, uninstall Firefox by following the steps mentioned in the Uninstall Firefox article.
IMPORTANT: On Windows, the uninstaller has the option to remove your personal data and settings. Make sure that you do not check this option; otherwise all of your bookmarks, passwords, extensions, user customizations and other Firefox user profile data will be removed from your computer.
After uninstalling Firefox on Windows, delete the "Mozilla Firefox" program folder, located by default in one of these locations:
(On 32-bit Windows)C:\Program Files\Mozilla Firefox
(On 64-bit Windows)C:\Program Files (x86)\Mozilla Firefox
Go to the Windows Start menu and click on "Computer".
In the Explorer window that opens, double click Local Disk (C to open the C:\ drive.
Find the "Program Files (x86)" folder or "Program Files" folder.
On 32-bit Windows, double-click the Program Files folder to open it.
On 64-bit Windows, you will see a "Program Files (x86)" folder AND a "Program Files" folder. Open the Program Files (x86) folder.
Look for a Mozilla Firefox folder. If you find one, right-click it and select Delete and confirm that you want to move the folder to the Recycle Bin.
Now, go ahead and reinstall Firefox:
Double-click the downloaded installation file and go through the steps of the installation wizard.
Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.