Handle DOM event in NPAPI plugin

Hi,

I am  a mozilla newbie and a windows developer.  I wrote a NPAPI
plugin and I need to catch and handle the DOM event, such as
BeforeNavigate2,  DownloadComplete event. Similar to providing
handlers to the windows WebBrowserEvents2. I also need an FF web
browser control to navigate to some URL. Can someone tell me how to do
this in NPAPI plugin? Thanks.