Microsoft Genuine Windows Validation process now works in Firefox and other Mozilla browsers. Firefox users can manually install the Windows Genuine Advantage validation Firefox plug-in available on Microsoft's website to complete the Windows validation process.
Microsoft Windows Genuine Advantage program is an online validation process that enables you to verify that your copy of Windows XP is genuine (non-pirated). You are prompted to validate your copy of Windows if you request a genuine Windows download from the Microsoft Download Center or Windows Update. The WGA Plug-in for Mozilla Firefox provides the same Windows validation as the IE ActiveX control.
Download: WGA Firefox plug-in
News source: Digital Inspiration