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Microsoft .Net Framework 3.5 SP1 Secretly Installs its Firefox Addon

February 2, 2009

Recently I got the Windows Update message about the newest .Net Framework 3.5 Service Pack 1. Have I installed 3.5 in my PC? No, I haven’t. Just 2.0 & 3.0 for some softwares I have (e.g. Paint.Net and CDBurnerXP). Should I need to upgrade from .Net Framework 2.0 & 3.0 (each is quite fatty) to 3.5?

Google a little bit, and I found this blog post. It turns out that this update installs not only the 3.5 SP1 but also the .Net Framework Assistant 1.0, aka the stealthy Add-on for Firefox, without telling you so. Worst, it disables the uninstall button.

This “auto-installation” was reported since last August. You can hack to uninstall this stealthy add-on by following the instruction from here.

For Windows XP SP3 users:

  • Open regedit (Windows Key -> Run -> regedit). Backup the registry or even the whole system if you want.
  • Go to”HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Firefox\extensions” and delete the key. This remove the unwanted extension
  • To clean the user agent, delete “general.useragent.extra.microsoftdotnet” & “microsoft.CLR.clickonce.autolaunch”
  • After that, you can remove the files of the extension are located in \WINDOWS\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation\DotNetAssistantExtension\

Since I haven’t installed the 3.5 SP1 (I check each of Windows Updates before the installation starts), I don’t go through these steps by myself. If you have doubts, please also check around.

A little bit complaint about .Net Framework. Why do the users need to install so many different versions so that the software based on the older version can work? I really don’t like the idea of having so many fatty versions installed in my PC.

If you’re interested in how to consolidate .Net Framework versions, check out the discussion here (Warning: just to understand it might give you some headache).

Update: I removed 3.0 SP1 and only keep 2.0 SP1, which is enough for Paint.Net & CD BurnerXP.

One Comment leave one →
  1. piles permalink
    April 16, 2011 4:10 am


    Je suis un utilisateur de magix video deluxe et pour l’utiliser entierement je dois installer net framework 3.5 sp1. Seulement il m’est impossible de l’installer, à chaque tentative c’est un échec. Je suis en sp3 windows xp pro. navigateur Firefox. Merci de me donner une solution.

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