Use Xpcom.CreateInstance(String); in VB.NET

Use Xpcom.CreateInstance(String); in VB.NET

I wann use such a CreateInstance-Function as the following one for GeckoFx
in VB.NET. Xpcom.CreateInstance("@mozilla.org/login-manager;1");
The code above works fine for C-Sharp but not for VB.NET, what should I
use instead?
If I try
Xpcom.CreateInstance(nsILoginManager)("@mozilla.org/login-manager;1") I
get an Error for as the following one :"This [nsILoginManager] is a type
and cannot be used as Expression"
What else should I write/use?
The reason why I try this is to activate the historisation for fields in
the webbrowser-component.