why isnt there a mouseclick event in the webbrowser method listbox?
Because the mouse click is sent to the web page shown in the control. Just like you normally click the web pages in your browser. The explanation above is not totally correct, but I think it's good enough ;)
I don't know why would you like to trap the mouse click, but you could try to use GotFocus event
Private Sub WebBrowser1_GotFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles WebBrowser1.GotFocus
MessageBox.Show("Click", "Click", MessageBoxButtons.OK, MessageBoxIcon.Information)
It does have its limitations compared to "normal" Click event.