I have found this plugin installed in my Firefox browser but I have not the faintest idea of its usefullness
WPI is part of the Microsoft Web Platform Installer package. For more information, please visit Microsoft at the following link:
Thanks for using Firefox!
The WPI file extension is associated with WCPUID and used for its plug-in files. WCPUID is an old program that displays the CPU information of your personal computer.(from:http://www.file-extensions.org/wpi-file-extension)
This is a really poor way to design a plug in without any easily visible references (Microsoft or otherwise) included in it. Shame.
You can find additional info in the registry under HKLM\SOFTWARE\MozillaPlugins\@microsoft.com/wpi,version=X.X. There's a "Vendor" value, and in this case, it does say "Microsoft".