If you can’t beat them, invade them – or something to that effect, right?

Microsoft installs, without asking, an extension in Firefox to “make things easier for users” and, I guess, to protect our children.

Thanks, Robert, for the instructions to remove it. Here is the short form:

Registry:

Delete
HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Firefox\extensions

in Vista 64-bit:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mozilla\Firefox\Extensions

Firefox: about:config in the address bar
set to empty string:  general.useragent.extra.microsoftdotnet
set to false  microsoft.CLR.clickonce.autolaunch.

Filesystem:
delete files under: \WINDOWS\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation\DotNetAssistantExtension\