HTML5 Extension for Windows Media Player Firefox Add-on

Martin Brinkmann
Dec 16, 2010
Updated • Dec 5, 2012
Firefox, Firefox add-ons

There is still some confusion surrounding HTML5 video formats and which browser supports which. Mozilla Firefox for instance does not support the H.264 video format which means that users who encounter videos encoded in the format will not be able to view them in the browser, unless the site that is offering them is offering the WebM codec as well which is supported by the web browser. But if there is not a fallback it means that the video cannot be played in Firefox.

That's a problem from a user perspective. The HTML5 Extension for Windows Media Player Firefox add-on by Microsoft tries to add support from H.264 videos in Firefox. The browser plugin only works in Firefox 3.6 or later and only under the Windows 7 operating system. In other words, Windows 7 users with Firefox 3.6 or higher can use the plugin, everyone else cannot.

But what is the add-on doing exactly?

The Extension is based on a Firefox Add-on that parses HTML5 pages and replaces Video tags with a call to the Windows Media Player plug-in so that the content can be played in the browser. The Add-on replaces video tags only if the video formats specified in the tag are among those supported by Windows Media Player. Tags that contain other video formats are not touched.

The add-on works on most pages that try to play H.264 video but not on all. Microsoft explains the issues that can be encountered the following way:

In some cases Firefox might fail to play a video even if the Add-on is correctly installed because the page might be using a call to canPlayType to determine if the browser can play H.264 content. Typically the check is done either using createElement('video') or getElementsByTagName('video') and then call canPlayType('video'mp4'). In both cases the call will return empty string even if the Add-on is installed and the browser could play H.264 videos.

Firefox users who want to watch H.264 encoded videos may want to try out the add-on to do so. Another option would be to switch to a web browser supporting H.264 natively, which is also the only option for non-Windows 7 Firefox users, at least at this point in time.


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  1. ogre said on January 4, 2011 at 8:11 pm

    Html Extension For Windows Media Player 1.0 causes FF 3.6.13 to close all windows when closing just one. browser.tabs.closeWindowWithLastTab = false doesen´t seem to help in this situation

  2. Squall said on December 21, 2010 at 7:51 am

    POS extension breaks firefox’s memory management.

    all the idiots who install it will be off blaming firefox for more memory leaks when its microsofts fault.

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