Current Version Plugin Microsoft® DRM
You may be wondering what this plugin is doing in your Firefox while you never installed it. It comes with Windows Media Player, not with Firefox itself.
Microsoft® DRM is also known as Windows Media DRM, it is a Digital Rights Management service for the Windows Media platform. It is designed to provide delivery of audio and/or video content over an IP network to a PC or other playback device in such a way that the distributor can control how that content is used.
This plugin does not harm you nor it affect your normal activities. This is to add support for Windows Media Player files with DRM enabled.
If you want to update Microsoft® DRM plugin, you may update you Windows Media Player or update manually by downloading dll files. Normally you do not need to do anything her, Firefox show warning because it does not recognize this plugin.