InetBgDL plugin
Kudos for this plugin, Anders. I think it has great usage potential, but it also has some serious issues. If connection drops, dl can't be restarted. Also, it takes a long time to unload when dl is canceled, sometimes even fails and leaves pluginsdir undeleted; on several occasions it completely hanged. The problem is that InetBgDL::Get /RESET /END doesn't seem to work properly - it takes long to complete and after that, new calls to InetBgDL::Get don't work.
Mozilla continued the development and their current version (github.com/mozilla/releases-mozilla-aurora/tree/master/other-licenses/nsis/Contrib/InetBgDL) works fine all around in my tests, but they only provide the Unicode version.
From your description given on nsis plugins site, I figure this plugin was an "on demand" job and is no longer in your focus of interest. Still, since it's hosted on nsis plugins and I tried it, I'm providing feedback.