Windows Media Player Plugin for Firefox allows you to view videos loaded into your computer including, playing streaming audio, video, animations and multimedia presentations on the web. So, without the Windows Media Player Firefox Plugin you are staring at a blank screen. 
Note: You will usually have similar issues cropping up anytime you try and view video files in Firefox using Windows Media format including, .wmv files.
Installation
When you don’t have the Windows Media Player Plugin installed for Firefox, all you need is to do is install it by downloading and running the plugin installer. The installation of the Windows Media Player Firefox Plugin may require administrative access to your PC. You must close all other open browser windows before continuing with the installation.You can download Windows Media Player Firefox Plugin from the website given below:
Verification
When you run through the quick installation wizard, you can verify if the Windows Media Player Firefox Plugin installation has actually worked. The easiest method of verification is to just open a Windows Media video, you can also type the following into the address bar to see the list of loaded plugins:
about:plugins
On typing the above path you will see the Windows Media Player Firefox Plugin in the list and you can also see how Firefox will use the Windows Media Player Plugin on which type of files. Now, you can view this Windows Media format video file in Firefox as the Windows Media Player Firefox Plugin installation has been successful.
Technical Notes
The following list will help you with troubleshooting the installation of Windows Media Player Firefox Plugin, provided you have any issues with this installer:
- The Windows Media Player Firefox Plugin uses the IE Proxy settings which is because the plugin itself is only a thin wrapper around Windows Media Player, which always uses IE internally to fetch data. It does not use the several plugins available in Firefox.
- The Windows Media Player Firefox Plugin files are installed to the “C:Program FilesMozilla Firefoxplugins” directory by default and the file name is np-mswmp.dll. You can manually delete this file if the uninstaller fails to remove it for whatever reason
- Also, you could copy the same .dll file in theory, into the Windows Media Player Firefox Plugin directory on any Firefox installation and it should work without running the installer.
Note: You can also get a plug-in that plays Windows Media Player videos on Ubuntu by installing the mozilla-mplayer package that works with Firefox, Opera and other browsers that support Mozilla plug-ins.