.NET Framework 3.5 SP1 in my Firefox browser? It is more likely than you think.

An extension called ".NET Framework Assistant" is installed for Firefox 3.x when you install .NET Framework 3.5 SP1. If you comb through some of the .NET 3.5 SP1 release notes, it is very briefly mentioned as adding ClickOnce support into your browser.

On the downside, the .NET 3.5 SP1 installer doesn't really come out and ask for permission to do so, and also seems to gray out the Uninstall button.


It also adds .NET user agent strings to your Firefox user agent string.


You can enable and disable ClickOnce support and how many versions of .NET the browser reports to web servers.


If you want to completely kill the extension, with Firefox closed, delete the folder %WINDIR%\Microsoft.NET\Framework\v3.5\Windows Presentation Foundation\DotNetAssistantExtension, and delete the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Firefox\extensions\{20a82645-c095-46ed-80e3-08825760534b}\.

I try to keep my Firefox profile as lean as possible, and I am not aware of many ClickOnce applications on the web yet, so I'm not really missing out on much by removing this for now.

Registry location found from a post here.