The Microsoft Windows Presentation Foundation plugin allows Firefox to view certain multimedia content on websites. This plugin was installed on many computers by Microsoft as part of a Windows update.

Recently, it was disclosed that this plugin has a major security vulnerability that can be exploited by malicious websites. Mozilla has added the plugin to the add-ons blocklist, which disables it in Firefox.

Disabling the Windows Presentation Foundation plugin

Mozilla has put the Windows Presentation Foundation plugin as an overridable blocklist item. This means that it is strongly recommended that you disable this plugin. You can do so multiple ways:

Disabling via the blocklist popup

When you start Firefox, you may be presented with a blocklist popup similar to the following:

Make sure the Disable item is checked and click Restart Firefox to disable the Windows Presentation Foundation and restart Firefox.

Disabling via the add-ons manager

You can also disable this plugin from the Add-ons Manager:

1. From the Tools menu, select Add-ons.
2. Select the Plugins panel
3. Select the Windows Presentation Foundation item and click Disable.

Disabling manually

You can also disable this plugin file manually:

1. Close Firefox by clicking on the File menu and selecting Exit.
2. Open Windows Explorer and navigate to C:\WINDOWS\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation\
3. Right-click on the NPWPF.dll and select Rename.
4. Change the file's name to NPWPF.dll-backup.

Enabling the Windows Presentation Foundation plugin

The security vulnerability is fixed by Microsoft's MS09-054 patch. If you need to use web content that relies on this plugin, and you have this patch installed, you can override the blocklist and enable the plugin.

1. Make sure you have installed the MS09-054 patch.

• • In Windows, click Start then Control Panel then Change or Remove Programs
  • Select the Show updates checkbox
  • Under Windows Internet Explorer 8 - Software Updates make sure that Security Update for Windows Internet Explorer 8 (KB974455) is installed.
    • Note: You may instead see Windows Internet Explorer 7 depending on your IE version number.
      
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1. Restart Firefox
2. From the Firefox Tools menu, select Add-ons
3. Select the Plugins panel
4. Select the Windows Presentation Foundation item and click Enable.