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Consider the following scenario:

  • You have the Microsoft .NET Framework 3.5 Service Pack 1 (SP1) and the hotfix that is described in Microsoft Knowledge Base (KB) article 971643 installed on a computer.

  • You have Mozilla Firefox 3.0 or a later version of the Web browser installed on the same computer.

  • The Windows Presentation Foundation (WPF) add-in for the Firefox browser is enabled.

  • You run an XAML browser application (XBAP) in the Firefox browser.

  • You resize the browser window.

In this scenario, the content of the XBAP is not resized to fit the browser window.


Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.


You must have the .NET Framework 3.5 SP1 installed to apply this hotfix.

Restart requirement

You do not have to restart the computer after you apply this hotfix if no instance of the .NET Framework is being used.

Hotfix replacement information

This hotfix does not replace other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

File name

File version

File size











Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

To enable the WPF add-in for the Firefox browser, follow these steps:

  1. Open the Firefox browser. Then, type about:config in the Address bar.

  2. Type blocklist into the search box.

  3. Double-click the extensions.blocklist.enabled preference to enable the preference.

  4. Restart the browser.

  5. Locate the Add-Ins item in the
    Tools menu, and then click the Add-Instab.

  6. Scroll down in the Add-Instab to the Windows Presentation Foundation item. If the item is unavailable, select it, and then click Enable.

For more information about the hotfix that is described in KB article 971643, click the following article number to view the article in the Microsoft Knowledge Base:

971643 FIX: You receive a "System.ComponentModel.Win32Exception" exception when you run a WPF Browser application to read or write a cookie in a Firefox Web browser

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