If you use portable applications like I do, you may get into situations with plugins.   Firefox popularity is driven by its plugins, but one special plugin that IE integrates is the Windows media player plugin or WMP plugin.  This assumes that you have the Windows Media Player already installed and functioning properly.  If not, then this plugin wont work for you.

You can get the WMP plugin from the here.  This plugin comes in the form of an installer.  This installer will be looking for the typical Firefox installation path, which is is usually "C:\Program Files\Mozilla Firefox".  If it is not there, then it will place the plugin in root folder of where you installed the plugin i.e "C:\PFiles\Plugins".

Well then, we need to go to "C:\PFiles\Plugins" and look for a file called "np-mswmp.dll".  This is our plugin.  You need to place this file into Firefox's plugin folder.  When you're done, restart your Firefox and you should be able to view online WMP videos.  If you can't find the plugin folder, do a search on it and you should be able to find it.