How to navigate to URL in Gecko SDK?

It's simple:

nsIWebBrowserChrome->GetWebBrowser(nsIWebBrowser**)

nsIWebBrowser -QI-> nsIWebNavigation
nsIWebNavigation->LoadURI(...)

See code: xulrunner-1.9.1.3-source\mozilla-1.9.1\embedding\tests\winEmbed\winEmbed.cpp, function OpenWebPage()