Uninstall Microsoft .NET Framework Assistant from Firefox

Hopefully, this info will save others time…

What is this Microsoft .NET Framework Assistant extension for Firefox? How did I get it? Do I need it?
Answers are here:

I uninstalled it 3 months ago, and I haven’t noticed any problems.

My steps to uninstall it reversibly:

  1. Login to the admin account
  2. Close Firefox
  3. Open regedit (Start > Run > “regedit”)
  4. Goto “HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Firefox\extensions”
    (or “HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mozilla\Firefox\extensions” for 64-bit versions of Windows)
  5. Left-click on the key “{20a82645-c095-46ed-80e3-08825760534b}” to highlight it.
  6. Save the key to a .reg file using the File > Export menu
  7. Right-click the key and click Delete
  8. Close regedit
  9. Restart Firefox and confirm the extension is gone.

If you need to restore the extension, close Firefox and double-click the .reg file that you saved above.

Thanks to this site for help: http://wyday.com/blog/2008/how-to-uninstall-microsoft-net-framework-assistant-from-firefox/


Edit: add instruction to close regedit

I installed .NET framework 3.5 when it came out. I saw that FF addon and went straight to System Restore. Then hid the update and never looked at it again. ;D

It’s ridiculous how you can’t even uninstall it in FF.

But thanks for sharing the tutorial. :slight_smile:

In case some are wondering why removing this is a good idea, here’s a quote:

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.

Leave it in at your own risk.

I just hit uninstall->Re-started and it was gone, will keep an eye out though.

Any opion on the Windows Presentation Foundation Plugin?


Unfortunately Matty, that won’t get rid of it. If you use the Nightly Tester Tools or Mr Techs toolkit to look at your configuration details, it’s still listed, even though it doesn’t show in the Addons list.

In fact, in addition to the instructions given by the OP you may also have to do the following:

  1. Open a new Firefox window, and in the address bar, type about:config and press Enter.

  2. Type microsoftdotnet in the Filter field to quickly find the general.useragent.extra.microsoftdotnet setting.

  3. Right-click general.useragent.extra.microsoftdotnet and select Reset.

  4. Restart Firefox.

  5. Open Windows Explorer, and navigate to %SYSTEMDRIVE%\Windows\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation.

  6. Delete the DotNetAssistantExtension folder entirely.

Nice 1 Toggie :-TU,

Had a look in about:config but it wasn`t there FX 3.5(b99)

Did take ownership and get rid of the DotNetAssistantExtension folder though so hopefully that will sort it.


Microsoft released a patch. See

Notice that the registry change from the first post must be reversed before applying the patch.

I am considering reversing my registry change and applying the patch to avoid potential problems with a future Windows Update that sneaks in the patch under some other title.

I would like to hear the experience of anyone with Firefox 3.0.11 and Windows XP who has tried the patch.
I would also like to hear comments in general about the patch before I apply it.

Method 2 of Microsoft’s instructions agrees with my original post and Toggie’s supplement:

If the user applies method 1 and then uninstalls the extension from Firefox’s Add-ons menu, is the same registry key deleted, Firefox configuration item reset and folder deleted as with method 2?

I don’t think I ever want the Microsoft extension back for Firefox, but, to be safe, I effectively implemented method 2 in a reversible way:

  1. Follow the instructions in my original post
  2. Record from about:config that general.useragent.extra.microsoftdotnet is a string=(.NET CLR 3.5.30729) before resetting the item (then restart Firefox).
  3. Rename the folder %SYSTEMDRIVE%\Windows\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation\DotNetAssistantExtension\ to .\DotNetAssistantExtension-disabled\

I realized that a registry cleaner could make the method in my last post non-reversible. This is because there are registry keys associated with the folder that was renamed. If you clean the registry before renaming the folder, then clean the registry after renaming the folder and save the deleted keys as a .reg file, you can later double-click on the .reg file to restore the registry. Otherwise, these keys would be lost in some future registry cleaning, and they might be difficult to find among a large list even if they were backed up.

Err … ;D 2 noobie questions here :-

  1. What is .NET Framework Assistant for ? And I can’t recall I have installed this addon but it IS in my FF addon list ? ???

  2. Is it sufficient to just disable it from addon list to prevent this “most dangerous vulnerabilities present in all versions of Internet Explorer ?”

What is .NET Framework Assistant for

From Microsoft:

In .NET Framework 3.5 SP1, the .NET Framework Assistant enables Firefox to use the ClickOnce technology that is included in the .NET Framework. The .NET Framework Assistant is added at the machine-level to enable its functionality for all users on the machine. As a result, the Uninstall button is shown as unavailable in the Firefox Add-ons list because standard users are not permitted to uninstall machine-level components. In this update for .NET Framework 3.5 SP1 and in Windows 7, the .NET Framework Assistant will be installed on a per-user basis. As a result, the Uninstall button will be functional in the Firefox Add-ons list. This update will also make this version of the .NET Framework Assistant for Firefox compatible with future versions of the Firefox browser. To properly update the .NET Framework Assistant, this update must be applied while the extension is enabled in Firefox. To remedy the result of installing this update while the extension was disabled, uninstall the update, re-enable the extension, and reinstall the update. Updates to the .NET Framework Assistant may include updates to the Windows Presentation Foundation Plug-in for Firefox causing it to be enabled upon its initial update.
And I can't recall I have installed this addon but it IS in my FF addon list ? Huh

You didn’t, Microsoft did!

2) Is it sufficient to just disable it from addon list to prevent this "most dangerous vulnerabilities present in all versions of Internet Explorer ?"

No, Please read the above or see this link:


Microsoft did!

:frowning: Invasion of privacy again.

:frowning: So helpless us Windows users.

Thanks Toggie.

Oh how much i wish to see Firefox take MS to courts, MS needs to stop adding its c**p to good things. It has no right.

Linux may just be the way of the future.

I now have upgraded to Firefox 3.5.2. I reversed my uninstall steps for the MS extension, and then I noticed in Tools|Add-ons|extensions that Firefox shows the extension with an exclamation point because it is not compatible with this version of Firefox. I then allowed Windows Update to install the extension update (http://support.microsoft.com/?kbid=963707). Now the MS extension was gone from the list, but was it really gone?

This web page displays the user agent string: http://www.netinfo.org.ua/
The suffix of mine was “(.NET CLR 3.5.30729)”, which is from the MS extension!

After doing some research, I found this page explaining that MS makes the extension hidden after the update:

This page explains all the places that Firefox extensions can hide:

With this info, I found that I had hidden extensions for MS .NET Framework Assistant and Java Console. I left the Java Console extension in place because the Java control panel has a setting to prevent it from starting.

I followed the same uninstall steps I used before, and I ran Windows Update again. It now showed KB963707 as a critical security update again! Since I didn’t delete the extension’s folder, I renamed it back to its original name. I ran Windows Update again, and now it didn’t offer the KB963707 update.

Since Windows Update will not re-install the MS extension into Firefox if the DotNetAssistantExtension folder is unchanged, my plan is to leave it alone and continue to take the MS security updates (blocking an update may cause a future update to break). Deleting the registry key (see original post) and the user agent (see Quill/Toggie’s post) successfully disables the MS extension. Since any software installation or update can install a Firefox extension, my plan is to keep a watch on the Firefox registry key and extension folder in the Program Files area for hidden extensions. I may also add them to the protected registry keys and folders in Defense+, but this has no effect when using Defense+'s installation mode.