Thanks guys. I went the route of disabling the listbox, since in my testing it seems DocumentComplete could potentially fire multiple times for the same web page. I used @Michel_Bujardet suggestion of using a timer in DownloadComplete here to combat that.
Is there any way to also disable the HTMLViewer? Setting the enabled property doesn’t work. And the problem I see is that as DownladComplete is firing, the user can click on and access the links that have already loaded up.