Solution to Common Xul.dll Errors

Xul.dll ? File Information

The xul.dll file is associated with the Firefox browser from Mozilla Foundation. This file is known to exist in 78,848, 3,481,440, 10,000,000, 6,668,288, 9,555,968, 11,764,224, and 8,278,016 file sizes.

In this article, we will discuss a few instances of xul.dll errors that typically occur when you try to open your Firefox browser.

Error 1

After upgrading to Firefox 3.0, when you try to open your browser, ?Firefox may crash and you may receive the following error

?Firefox.exe – Bad Image
C:\Program Files\mozilla Firefox\xul.dll is either not designed to run on WINDOWS or it contains an error. Try installing program again.?


To fix this xul.dll error, perform the following steps in the sequence they appear.

      1. Reinstall Firefox: Uninstall Firefox, remove all its folders, and then reinstall Firefox 3.0 in the root directory (typically it is C:) and not in Program Files folder. On a Windows PC, you may use either the built-in Add or Remove Programs utility, or a reliable third-party tool, such as Perfect Uninstaller to uninstall Firefox.
      2. Uninstall ?Download Embedded? Plugin: If the xul.dll error still persists and you are able to open Firefox browser, uninstall the Download Embedded plugin to resolve the issue. To achieve this, perform the steps illustrated below:
        1. In the Firefox window, open the Tools menu, and select Add-ons to open its corresponding window.
        2. Next, in the Add-ons window, select the Extension panel to view the installed extensions.
        3. Next, select Download Embedded and click the Uninstall button.
        4. Restart your Firefox browser.
      3. Disable AVG Search 8.0: If you have installed AVG Search 8.0 on your computer, disable it and see if the error stops occurring.
      1. Perform a memory test: If the above steps fail to resolve the issue, run a memory check using a reliable Memory Diagnostic tool.
      1. Perform a malware scan: Last, but not least, run a malware scan using advanced security software, such as STOPzilla Antivirus and Spyware Cease to ensure your DLLs and other files are not infected.

If you are still getting the error after you perform the above steps, we recommend that you either switch to a previous version of Firefox or install a different Internet browser.

Error 2

When you try to open a Firefox browser, you may receive the following error:

?XUL.DLL is not valid without reinstall?


To fix the xul.dll error, first browse to the Mozilla Firefox folder. Next, locate the xul.dll file and rename it to xul.dll.old. Now, find the xul.dll.moz-backup file and rename it to xul.dll. Finally, restart your Firefox browser.

If the above steps fail to fix the xul.dll error, reinstall Firefox. Before, you reinstall Firefox; ensure that you remove all the files related to previous Firefox installation. To do this the right way, use an efficient third-party uninstaller tool, such as Perfect Uninstaller to perform a complete removal of Firefox.

Error 3

When you try to open a Firefox browser, the browser window may not open and you may receive the following error message:

?firefox.exe – Unable To Locate Component

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


To rectify the this xul.dll error, reinstall Firefox on your computer.