I hope to have the next two sections completed sometime this week (although I must be honest and say that I haven't started work on them yet). The content won't be drastically different than what the older tutorial has, but I do plan on cleaning things up. I'm glad you enjoy it! :D

I do expect to slim down the tutorial somewhat (hopefully), but keep in mind that this 1.5 tutorial will be replacing the current tutorial. As such, the majority of the content will remain intact. I am planning on writing an "advanced" toolbar tutorial, covering some higher level topics: using a single image sheet (instead of multiple images), moving your toolbar around in the browser, autocompletion (possibly), and more.

As enc noted, you can indeed make use of the other sections of the old tutorial. However, note that skin registration is one of the changes in Firefox 1.5 that I have not yet covered, so the information in the old tutorial is "out of date" in that regard. I may also move the "dynamic development" section somewhere closer to the front in this newer release of the tutorial ... it's a helpful addition to 1.5 that cannot be overlooked.

A "skin" is simply a collection of style rules (implemented via CSS) and possibly some images to alter the look of an extension. The old skin registration mechanism involved creating a contents.rdf file down in the skin folder. In 1.5, the registration takes place in the chrome manifest. All of this will be explained in chapter 5 of the tutorial.