How to remove Microsoft .NET Assistant from Firefox

Updated: February 7, 2009; May 30, 2009

Important notice: Microsoft have released an update to .NET Framework 3.5 SP1 for the .NET Framework Assistant 1.0 for Firefox, which addresses several compatibility issues with the Firefox browser. In this update for .NET Framework 3.5 SP1 and in Windows 7, the .NET Framework Assistant is installed on a per-user basis and as a result, the Uninstall button is functional in the Firefox Add-ons list. This makes .NET Assistant a valid, fully uninstallable utility and therefore, the methods listed in this article are no longer relevant or might not be needed. You may also want to take a look at Microsoft's official manual removal guide. Thanks.

May I call this thing spyware? I think I can. Because spyware fits two clear definitions: Installs without explicit user consent. Cannot be uninstalled using its own uninstaller or via Add/Remove.

So, the story begins with a Microsoft .NET Framework 3.5 SP1 update (KB951847) recently launched. In case you decide to download this update, either automatically or manually, you will end up with a new Firefox extension (if you're using this popular browser), which you have not asked for. OK, no problem, uninstall it. Ah ...


I decided to test this quite worrying story and verify the results for myself. And then, write an article / tutorial that explains how the problem occurs and how you can solve it.

Statement of problem

Claims are as follows: Microsoft / Windows .NET Framework 3.5 SP1 update (KB951847) will install a new extension, specifically .NET Framework Assistant 1.0, to your Firefox browser, if you have it installed, without user consent. Furthermore, to make things worse, this extension cannot be uninstalled.

Is this true?

Let's see ...

Test case - install .NET 3.5 framework

I went to the Microsoft website and downloaded the package. Double-clicked to install.

Begin install

The installation begins. I used System Safety Monitor (SSM) to monitor all system and registry changes that .NET 3.5 installation makes to see whether I'll see anything suspicious, especially related to Firefox.

The installation seems to proceed well, except the constant alerts from SSM, informing of numerous registry changes. So far, there's nothing major happening.

Installation in progress

A thousand SSM alerts later, the installation is complete. I fired up Firefox to see whether new extensions have been added. Nope.

No assistant

But this does not conclude my case. We now have to perform a Windows Update and see whether the latest patch causes any issues.

Windows Update

Indeed, there's a high-priority update (first on the list) for .NET Framework, our beloved KB951847. It has been automatically selected and would have been automatically offered had I been using automatic updates.

Nothing mentions Firefox in any way. Furthermore, if you check the KB951847 page, it lists the changes introduced in the Service Pack, but nowhere does it mention Firefox, either.

The download is a whooping 250MB, which raises a question whether you should be using this in the first pace. But let's proceed.


After an age of prompts, the installation is complete. I did not notice any prompt from SSM telling me of any change about to happen with Mozilla Firefox, but I could have easily missed it in the torrent of changes. Well, following a restart, I check my Firefox browser and:

Microsoft .NET Framework Assistant 1.0 has been installed

Notice that the Uninstall button is grayed out. I was not asked to approve or even confirm this installation. There is no mention that this thing was going to be installed, neither on the Microsoft pages or during the installation itself. And now, it seems, it cannot be removed.

Spyware, anyone?

Assistant installed

Removing Microsoft .NET Framework Assistant 1.0

Luckily, this thing can be removed, rather easily.

Solution 1: Simply delete a few files

This is relatively easy and takes only about 2 minutes. There's no need to be specially savvy about computers. Anyone can do this. First, close Firefox. Now, navigate to the following folder:

Windows Presentation Foundation\DotNetAssistantExtension

Like this:


Move, rename or delete the files inside this folder. If you want to retain some sort of a backup, then zip or rar the files away. You can also delete them or rename them. But make sure once your job is done to leave this folder empty.

Start Firefox. The spyware should be gone.



The next step is to clear away the user agent the .NET Assistant leaves behind. If you don't know what a user agent is or how to use the Firefox configuration tab called about:config, you can skip this step.

In Firefox, in the address tab, type about:config and hit Enter. This will take you to a Firefox configuration page, where you can control different aspects of behavior of your browser. The use of this page should only be done by skilled users.

Search for the following string: general.useragent. One of the results that will come up will be general.useragent.extra.microsoftdotnet. We want to reset this string.

Remove crud

Simply right-click it and choose Reset. Like this:


Job done. I would like to thank chrisretusn for this solution. It's simple, fast and elegant.

Solution 2: Registry hack

If you are skilled enough to edit the registry, then you can try this method, too. Again, first close Firefox. Then, open the registry editor (regedit):

Start > Run > regedit.exe

Now, navigate to:


Here, you will find an entry named {20a82645-...}. Under the Data column in the right pane, you can see and verify that it belongs to Microsoft .NET 3.5. Now, simply right-click this entry and delete it. If you want, export the key first as a sort of backup. Job done.



I like Microsoft products overall, but I cannot and will never condone blatant misuse of corporate power to distribute useless, unasked-for software to masses who do not have the skills to tell part good from bad or how to handle issues like the above.

The Assistant, if at all, should be an optional package, with clear user consent granted before any installation. Furthermore, the installation should be fully 100% revocable, so that anyone using the computer can do it, via the standard Add/Remove panel.

This is a very serious breach of user trust. Not only is this package delivered without explicit approval, it's also made difficult to remove. Moreover, its use is not clear. Lastly, the change affects third-party software, not one of Microsoft products, so the question is, what the hell did Microsoft want to achieve with this nebulous, spyware-like update? Animosity from a few trusted users? Force people not to install updates or use older versions of their products?

Anyhow, I leave big questions to big people. If you want this thing off your computer, then you have two rather fast and simple methods. Enjoy. And tell your Firefox friends.