How to control web address of Netscape6 (Gecko) ?

My project has some partwhich control the fuction of web browser, i.e. making browser to redirect to the assigned URL. I use Visual Basic as a development tools to control web browser via Win32 API. I use SendMessage function to control Netscape 4.77 as in the following details:

SendMessage edithWnd, WM_SETTEXT, 0&, ByVal url_redirect
PostMessage edithWnd, WM_KEYDOWN, VK_RETURN, ByVal CLng(0)
PostMessage edithWnd, WM_KEYUP, VK_RETURN, ByVal CLng(0)

'the variable "edithWnd" is the window handle of object which has Class name called Edit.

I've been trying to apply above to Netscape 6 (Gecko). It cannot send value to Edit. It makes me cannot redirect to assigned URL.

Please give me some knowledge about these. :D