WebBrowser ignores the code - vb.net

Question

I am trying to use Mibbit irc in my project, and so far is working well, but there is a flaw. Links pasted in the chat upon click are getting opened in Internet explorer, instead of users' default web browser. I tried implementing a simple code, but half of it seems to get ignored.
http://i.stack.imgur.com/FKGGr.jpg
WebBrowser Component Startup page: http://widget.mibbit.com/?settings=4abcd3a5f0bf25306d4c6d1968e28cb2&server=irc.mibbit.net&channel=%23Mytestchannel12345
Ignore if contains: mibbit.com(the chat widged) & ad4game.com(the stupid banner...)
If contains because it places different banners - thus, different links. As well for the widged, it obviously have several servers that is hosting it on and it redirects to some of them, like widged1.mibbit.com, widged2.mibbit.com, etc.
Open in Default user browser: All, except those 2 above.
Public Class Form1
Private Sub WebBrowser1_Navigating(ByVal sender As Object, ByVal e As System.Windows.Forms.WebBrowserNavigatingEventArgs) Handles WebBrowser1.Navigating
Dim navTo As String = e.Url.ToString
If Not (navTo.ToLower.Contains("mibbit.com") OrElse navTo.ToLower.Contains("ad4game.com") OrElse navTo.ToLower.Contains("about:blank")) Then
e.Cancel = True
System.Diagnostics.Process.Start(e.Url.ToString())
End If
End Sub
End Class
Nothing so far worked...

Answer 1

Okay, I've updated your code sample:
Add a new function to find out what the path to the default browser is:
Public Class Form1
Private Sub WebBrowser1_Navigating(ByVal sender As Object, ByVal e As System.Windows.Forms.WebBrowserNavigatingEventArgs) Handles WebBrowser1.Navigating
Dim navTo As String = e.Url.ToString
If Not (navTo.ToLower.Contains("mibbit.com") OrElse navTo.ToLower.Contains("ad4game.com") OrElse navTo.ToLower.Contains("about:blank")) Then
e.Cancel = True
System.Diagnostics.Process.Start(GetDefaultBrowserPath, e.Url.ToString())
End If
End Sub
' get the default folder path from the registry
Public Function GetDefaultBrowserPath() As String
Dim defaultbrowser As String = My.Computer.Registry.GetValue("HKEY_CLASSES_ROOT\HTTP\shell\open\command", "", "Not Found")
Return Split(defaultbrowser, """")(1)
End Function
End Class