gistfile1.cs

protected override void OnActivated(IActivatedEventArgs args)
{
    if (args.Kind == ActivationKind.Protocol)
    {
        ProtocolActivatedEventArgs eventArgs = args as ProtocolActivatedEventArgs;

        WwwFormUrlDecoder decoder = new WwwFormUrlDecoder(eventArgs.Uri.Fragment);

        string fbAccessToken = decoder.GetFirstValueByName("#access_token");
        
        /* Now you can use the access token to interact with the Facebook API */
    }
}