Well this is only part three, we are still just getting started after all =] so since I have very little time today I thought that I would write about how to include a icon for your restartless extension, since it's not exactly obvious. Although this method is documented here.
Basically all you need to do is include a icon.png in the root of your xpi (the same place as your bootstrap.js and install.rdf) and Firefox will automatically find it. You can also include a icon64.png in the root of your xpi and this will be used in the add-on manager's add-on detail view, so it's a good idea to include both if you have them because it'll be a better UX.
If you want to use the icon in other places use the method that I described in part 2 in order to find the file: url of the image and use that.