Remember back when Chrome cut support for H.264 video in favor of WebM? Well, yesterday the final build of IE9 was released, and it didn’t include support for WebM. Google saw this coming, and so they’ve already started work on a extension for IE9 that will add in WebM compatibility. The extension is still in the testing phase, but Google has got it up and running.
You can pick up the the WebM extension from the Google Tools site. Installation should only take a few seconds, and then it will disappear into the void only to emerge when you need to play WebM content. Note that this is an experimental build, so there are still a few bugs –see the full list of known issues for the plugin (the list is empty as of the time of writing this).
Incase you missed the download link above; Download the IE9 WebM extension.