This update rollup addresses issues of the Microsoft .NET Framework 3.5 Service Pack 1 (SP1) and of the Microsoft.NET Framework 2.0 Service Pack 2 (SP2) on a computer that is running Windows XP or Windows Server 2003. If you run partial-trust Windows Presentation Foundation (WPF) XAML browser applications (XBAPs) in the Mozilla Firefox browser, this update rollup disables the Web Browser ActiveX control (WebOC) in the Microsoft .NET Framework 3.0 SP2.
This update is a rollup comprised of KB976576 and KB977354. On some Windows Server 2003 Standard installations, it will fail to install and you will need to download it from here and install outside of the Windows Update service. If you install the rollup on a computer that already has .NET 4 then you probably won’t see KB976576 installed under Add/Remove Programs.