LINUX Users, HELP! Windos Media Player!!!?

I want to watch a video in the internet. But the browser(firefox) gives a message that I need to install windows media player. I try to install it but it says I have to doing manually. I go to microsoft web site. And of course the do not have WMP for linux. So the file is in wmv. How can solve this problem so I can see videos that require WMP or have the format wmv. Plz. HELP