This add-on won't work with Australis, because there's no Firefox menu button anymore.
The tools menu contains a lot of useful items, most of which have been incorporated into the Firefox menu button, but what the tools menu is most commonly used for are extensions. This extension adds a button, which contains the items of the tools menu, next to the Firefox menu button. It is possible to customize which items are hidden and which are shown.
The tools icon is a modified icon from here: http://www.gentleface.com/free_icon_set.html.