A step-by-step guide on how to get WMP embedded files to play in Firefox. It involves using this extension to enable ActiveX controls on a Firefox-rendered page.
The sweet part of the plugin is that you can whitelist ActiveX controls, meaning you can specify which ones you'll allow to run on your machine while blocking all others. For 1.0 of Firefox it defaults to only whitelisting the WMP plugin.
While this seems secure, I can't escape the feeling that I'm unsecuring Firefox to the same level as IE.