Remove the Microsoft .NET Framework Assistant (ClickOnce) Firefox Extension
Intended For
Windows 2000
Windows 7
Windows XP
Windows Vista

The Microsoft .NET Framework 3.5 Service Pack 1 update, pushed through the Windows Update service to all recent editions of Windows in February 2009, installs the Microsoft .NET Framework Assistant firefox extension without asking your permission.

This update adds to Firefox one of the most dangerous vulnerabilities present in all versions of Internet Explorer: the ability for websites to easily and quietly install software on your PC. Since this design flaw is one of the reasons you may've originally choosen to abandon IE in favor of a safer browser like Firefox, you may wish to remove this extension with all due haste.

Unfortunately, Microsoft in their infinite wisdom has taken steps to make the removal of this extension particularly difficult - open the Add-ons window in Firefox, and you'll notice the Uninstall button next to their extension is grayed out! Their reasoning, according to Microsoft blogger Brad Abrams, is that the extension needed "support at the machine level in order to enable the feature for all users on the machine," which, of course, is precisely the reason this add-on is bad news for all Firefox users.

Here's the bafflingly-convoluted procedure required to remove this garbage from Firefox:

Open Registry Editor (type regedit in the Start menu Search box in Vista/Windows 7, or in XP's Run window).
Expand the branches to the following key:
On 32-bit systems: HKEY_LOCAL_MACHINE \ SOFTWARE \ Mozilla \ Firefox \ Extensions
On x64 systems: HKEY_LOCAL_MACHINE \ SOFTWARE \ Wow6432Node \ Mozilla \ Firefox \ Extensions
Delete the value named {20a82645-c095-46ed-80e3-08825760534b} from the right pane.
Close the Registry Editor when you're done.
Open a new Firefox window, and in the address bar, type about:config and press Enter.
Type microsoftdotnet in the Filter field to quickly find the general.useragent.extra.microsoftdotnet setting.
Right-click general.useragent.extra.microsoftdotnet and select Reset.
Restart Firefox.
Open Windows Explorer, and navigate to %SYSTEMDRIVE%\Windows\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation.
Delete the DotNetAssistantExtension folder entirely.
Open the Add-ons window in Firefox to confirm that the Microsoft .NET Framework Assistant extension has been removed.

It will be a great day when PC users no longer have to waste this much time to protect themselves from those who write the software they use. (And if you're thinking, "Why not just use a Mac," may I remind you of the MobileMe junk recently installed on so many Windows machines without their owners' permission!)