Microsoft Media Player Plugin?

Ok, so I went to and I wanted to view a video in Windows Media Player, FireFox automatically wanted me to install missing plugins. So I let it search for a plugin and it said "Unknown Plugin" then, "Manual Install" so I clicked "Manual Install" and it took me to a Microsoft page for Windows Media Player downloads. I started to download the most recent release of Windows Media Player, but almost instantly it said something on the lines of, "A more recent version of Windows Media Player has been detected, installation cannot continue." So, does anyone know how to fix this problem?

Thanks in advance.

P.S. I'm running Windows Vista BETA 2 Build 5384

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