HTML5 Video and Interoperability: Firefox Add-On Provides H.264 Support on Windows

As you know, Microsoft is committed to interoperability, and the IE team has previously blogged about and provided developer previews and samples showing “Same Markup” – the same HTML, CSS, and script working across browsers – in action.

Today, as part of the interoperability bridges work we do on this team, we’re making available a new Firefox add-on that enables Firefox users on Windows to play H.264-encoded video on HTML5 by using the built-in capabilities found in Windows 7.

Microsoft has already been offering for several years now the Windows Media Player plug-in for Firefox, which is downloaded by millions of people a month who want to watch Windows Media content.

This new plug-in, known as the HTML5 Extension for Windows Media Player Firefox Plug-in, is available for download here at no cost.

It extends the functionality of the earlier plug-in for Firefox, and enables web pages that that offer video in the H.264 format using standard W3C HTML5 to work in Firefox on Windows. Because H.264 video on the web is so prevalent, this interoperability bridge is important for Firefox users who are Windows customers.

H.264 is a widely-used industry standard, with broad and strong hardware support. This standardization allows users to easily take what they've recorded on a typical consumer video camera, put it on the web, and have it play in a web browser on any operating system or device with H.264 support, such as on a PC with Windows 7.

H.264 is also a very well established and widely supported video compression format, developed for use in high definition systems such as HDTV, Blu-ray and HD DVD as well as low resolution portable devices. It also offers better quality at lower file sizes than both MPEG-2 and MPEG-4 ASP (DivX or XviD).

The HTML5 Extension for Windows Media Player Firefox Plug-in continues to offer our customers value and choice, since those who have Windows 7 and are using Firefox will now be able to watch H.264 content through the plug-in.

Microsoft is already deeply engaged in the HTML5 process with the W3C as we believe that HTML5 will be important in advancing rich, interactive web applications and site design.


Claudio Caldato,

Principal Program Manager, Interoperability Strategy Team

Comments (12)

  1. BenGillam says:

    hi , where can i send a bug report? the addon seems to cause popup windows (eg facebook share) to invoke firefox quit system – the save&quit/quit/cancel one when closed or self closed by javascript. you can hit cancel and cary on fine. when i removed addon normal behavior resumed.


  2. qs7000 says:

    The add-on is incompatible with Firefox 4 beta 10. When can we expect an update that fixes this?

  3. @ Funy1 This is a known issue with the FireFox SDK version we used ( We will roll out an update as soon as the bug is fixed.

  4. @qs7000 maxVersion was set to the latest beta version available when we released the add-on (4.0b8pre). I updated the xpi package so you should be able to installed in on FF 4.0B10 (test and it is working on my machine).

  5. SAPIE says:

    why dont there seem to be any place to get help for beginers /why there so many bugs for something new

  6. Ed says:

    This addon is believed to cause issues with Firefox 4 and

    Please see here for more info:

  7. Jacob says:

    @Claudio any update regarding the FF SDK bug and releasing a fixed add-on?

    its pretty annoying, if I have more then one FF window open and closes one of them I get the quit warning…

    but I suspect you depend on mozilla to fix it 🙁 anyway this add-on will be disabled until an update is released :/

  8. @Jacob, unfortunately it is a bug in the Mozilla SDK version we used (details at, I'll check if the bug is fixed in FF 4.0beta10, if so we can release an update quickly.

  9. @Ed Thanks for reporting the issue. I was able to repro the problem, I'll investigate and report back with my findings.

  10. marko says:

    doesn't work with firefox 4.

  11. Jan P says:

    This add-on is incompatible on Firefox 4 (stable). Is there coming new update to this add-on which fix this issue?

  12. @ Marko @ Jan P: a new version of the Add-on that supports FF 4.0 official release will be available in the next couple of days. Running few more tests and it will be available on the InteropBridges Add-On page (

Skip to main content