To safely remove the Microsoft .NET Framework Assistant from Mozilla Firefox, you must use Windows Registry Editor or file deletion, because Microsoft originally designed the extension to lock its “Uninstall” button within the Firefox Add-ons manager.
Follow these steps to safely and completely clear the extension from your system. Step 1: Remove the Windows Registry Entry
Because the extension was installed at the system level via Windows Update, removing its registry key unlocks or completely removes it from Firefox. Close Mozilla Firefox completely.
Press Windows Key + R to open the Run dialog box, type regedit, and press Enter.
Navigate to the following path depending on your Windows version:
For 32-bit Windows: HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Firefox\Extensions
For 64-bit Windows: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mozilla\Firefox\Extensions
Look for a registry key named {20a82645-c095-46ed-80e3-08825760534b} in the right pane. Right-click that entry and select Delete. Step 2: Delete the Core Extension Files
Manually clearing the remaining files prevents the extension from trying to re-verify itself. Open Windows Explorer (Windows Key + E).
Paste the following path into your address bar and hit Enter:%SYSTEMDRIVE%\Windows\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation</code> Locate the folder named DotNetAssistantExtension.
Right-click the folder and select Delete to eliminate it entirely. Step 3: Clean Firefox Config & Reset UserAgent
The assistant alters your Firefox UserAgent string to track deployment, which can be safely reset internally.
Open Firefox and type about:config into the address bar, then press Enter.
Accept the warning message to proceed to the advanced configuration menu.
Use the search/filter bar to find: general.useragent.extra.microsoftdotnet Right-click that specific preference entry and click Reset. Restart Firefox to apply all modifications smoothly.
For alternative instructions, the official process can also be referenced via the Microsoft Support Page.
Are you experiencing any other stubborn add-ons that won’t uninstall normally, or would you like assistance checking your browser UserAgent string to ensure it’s fully cleaned up? How to remove the .NET Framework Assistant for Firefox