How to Fix Xpcom_core.dll not Found Error

Xpcom_core.dll is a module that is associated with Mozilla Foundation?s Firefox.

Error Message

You may get an error message that looks like the one below upon opening Firefox:

This application has failed to start because xpcom_core.dll was not found. Re-installing the application may fix this problem.


If you are experiencing this problem, you might resolve the issue using the following methods.

Method 1

  1. Go to your Mozilla directory.
  2. Locate npmozax.dll.
  3. Delete npmozax.dll.

Method 2

  1. Save your profile.
  2. Uninstall Mozilla Firefox.
  3. Reboot your machine.
  4. Reinstall the browser.

Method 3

If you are using Windows XP, do the following.

  1. Copy the following files from C:\Program Files\Mozilla Firefox:xpcom.dll
  2. Place the files you copied into the C:\WINDOWS\system32 folder.
  3. Reboot your computer.
  4. Check to see if the error message appears again when you open Mozilla Firefox.
  5. If the error message no longer appears, consider yourself done.
  6. If the error message continues to appear, proceed to the next step.
  7. Place the files you copied into your Windows folder to make the error go away.

Method 4

  1. Backup your profile data.
  2. Uninstall Firefox.
  3. Download the Firefox installation package.
  4. Delete the C:\Program Files\Mozilla Firefox folder from your system.
  5. Reinstall Firefox.

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