Windows Validation plugin not compatible with FxP
The plugin installer can't detect the browser installation directory. Or, if Firefox is already installed on the host machine, it will likely install the plugin to the regular Fx installation.
http://www.microsoft.com/downloads/MozillaValidation.aspx?familyid=0a9b6...
There is an alternate validation method (browser independent), so this is just a heads-up.
I just prefer minimalist software that does the job right without alot of hassle or garbage left behind. But lately I've had problems that have me befuddled.