I’ve just finished my initial pass at the article Locating DOM elements using selectors. It provides a quick overview of what selectors are, as well as some simple examples, and refers the reader to the more specific documentation provided in the Gecko DOM Reference.
As always, please take a look and let me know — or correct it — if any errors or deficiencies are found.
With this, all major articles for Firefox 3.1’s documentation are complete. From here on out, it’s all about touching up existing material to cover updated APIs and the like.