Windows users: Have you noticed a new .NET extension in your addons menu?
This can be potentially a security risk (ahem, IE), so the Firefox Extension Guru has steps to remove it:
http://ffextensionguru.wordpress.com/2009/02/08/how-to-remove-microsoft-...
or
http://➹.ws/邗
It can run "ClickOnce" apps, but "ClickOnce" apps can contain spyware and/or viruses.