Is it looking for the Windows Media Player? The default installation of WMP does not include the Firefox plugin. There is a WMP plugin created by Microsoft for Firefox, but the standard WMP plugin installer from Microsoft is for Windows XP and Vista, though you can run the installer on Windows 7 it installs the plugin in a location that Firefox 4 will not find. One way to get around this is to install the HTML5 Extension for Windows Media Player Firefox Plug-in available from http://www.interoperabilitybridges.com/html5-extension-for-wmp-plugin That add-on will do 2 things, it will install the WMP plugin in a location that Firefox 4 on Windows 7 can find, it will also add an extension to add extra features for use by the Windows Media Player. This extension has been reported as causing memory leaks so I recommend that once you install the HTML5 Extension for Windows Media Player Firefox Plug-in you should restart Firefox then uninstall the extension. Uninstalling the extension will not remove the plugin, so Firefox 4 will still be able to use it.