Microsoft has shown its commitment to HTML5 in Internet Explorer already, with their countless demos and support in their upcoming IE9 browser, however it seems their support extends beyond Internet Explorer.
Microsoft has released a new add-on for Firefox that will make the browser capable of playing back H.264 video by tapping into the codecs installed on the system. It uses the Windows Media Player plug-in to play back video. Obviously it will work only on Windows, only Windows 7 in fact.
[RELATED_ARTICLE]The add-on looks for instances of HTML5 video, and replaces the video with an instance of the Windows Media player plug-in, pointed to the same video source file. Since the video in not actually playing in the browser itself, but in a plug-in, this has no advantages over just using the Flash Player.
Mozilla has been stringent about not supporting H.264 for HTML5 video in Firefox, and for good reason. While H.264 is popularly supported as an HTML5 video format and supported as such in Google Chrome and Apple Safari, it is in fact not part of the HTML5 standard, which is still mute when it comes to a standard video format for the web. H.264 has considerable licensing restrictions that make it not only the wrong choice as a format for the open web, but also expensive for companies such as Mozilla to use in their browser. It is another matter entirely for Google, which has no dearth of money, or for Apple and Microsoft, both of whom are licensors of patents used in H.264, and thus stand to gain from its adoption.
Mozilla, and Opera Software have instead decided to stand behind WebM and Theora as future standards for the web. In any case WebM is a better contender for the format of choice on the web in the future than H.264 due to its open nature.
If you are looking for the converse, i.e. HTML5 support in Internet Explorer, that too exists in the form of a codec pack by Xiph ‒ the creators of Ogg. This codec pack includes an optional component that adds support for the HTML5 video tag, with support for WebM / VP8 and Ogg Theora video, as an ActiveX plug-in for Internet Explorer.