Microsoft .NET Framework Assistant

To safely remove the Microsoft .NET Framework Assistant, you must delete its registry key and remove its extension directory, as the standard “Uninstall” button in Firefox is typically grayed out. This old component was an add-on bundled with .NET Framework 3.5 to deploy ClickOnce applications through Mozilla Firefox. Step 1: Remove the Windows Registry Key

You must have administrative privileges on your computer to complete these steps. Press Windows Key + R, type regedit, and press Enter.

Navigate to the following subkey depending on your operating system architecture:

32-bit Windows: HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Firefox\Extensions

64-bit Windows: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mozilla\Firefox\Extensions

Locate the value named {20a82645-c095-46ed-80e3-08825760534b} in the right pane. Right-click it, select Delete, and confirm the action. Step 2: Delete the Extension Files

Removing the registry key unlinks the extension, but you should clear the files from your storage drive to remove it completely. Close Mozilla Firefox entirely.

Open File Explorer and navigate to this folder path:%SYSTEMDRIVE%\Windows\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation

Delete the folder named DotNetAssistantExtension along with all of its contents. Step 3: Reset the User Agent in Firefox (Optional)

The extension alters your browser’s user agent configuration string. You can return it to its default state using the following process:

Open Firefox, type about:config into the address bar, and press Enter.

Accept any warning screens regarding advanced configuration settings. Type microsoftdotnet into the search filter field.

Right-click the preference named general.useragent.extra.microsoftdotnet and click Reset. Restart your browser. How to Update

You do not need to update or replace the assistant. Modern versions of Mozilla Firefox automatically block legacy extensions of this type due to structural security changes. If you require modern .NET functionality for development or running tools on your machine, you should manage your modern frameworks by installing official SDK updates from the ⁠Microsoft .NET Download Portal instead of maintaining old legacy browser plugins. If you are running into specific issues, let me know: What version of Windows are you currently using?

Are you trying to fix a browser error, or are you working on a developer project upgrade?

I can provide more targeted troubleshooting steps based on your goal! Microsoft Support How to remove the .NET Framework Assistant for Firefox