Firefox exe is not a valid win32 application

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This article explains what steps to take if you receive the error: "C:\Program Files\Mozilla Firefox\firefox.exe is not a valid Win32 application."

Clean re-install

  1. Open your system \TEMP\ folder.
    • (Windows Vista) Click the Windows Start button, and type %TEMP% in the Start Search box near the bottom of the Start menu, and press Enter.


    • (Windows 2000 and XP) Click the Windows Start button, and select Run..., then type %TEMP% and click OK.


  1. Hold down the Ctrl key as you press A, to select all items in your TEMP folder.
  2. Press Del to delete all items in your TEMP folder.
  3. Go to to download a new Firefox installer.
  4. Re-install Firefox, using the instructions at How to install Firefox on Windows.

Disabling all real-time anti-virus software

If you have any real-time anti-virus software, it should be disabled when downloading and installing Firefox.

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