<A target="_blank" href="http://port25.technet.com/archive/2010/12/15/html5-video-and-interoperability-firefox-add-on-provides-h-264-support-on-windows.aspx">Microsoft has released the HTML5 Extension for Windows Media Player</A> Firefox Plug-in to allow H.264 videos to be viewed in Firefox on Windows machines. This page includes a link to the download.