There is another change happening in Firefox. This is not as big as Australis, but it could affect some people.
The Panorama/Tab Groups feature of Firefox is being split off into an addon. This is that feature where you either press the Tab Groups button or press Ctrl-Shift-E, and you see all your tabs in a box. It allows you to group your tabs in other boxes, and then only see one group of tabs at a time.
If you don’t know what I’m talking about, don’t worry about it. But, if you use it, you’ll want to install the Tab Groups addon ASAP–before you upgrade to Firefox 45 (which comes out tomorrow). If you don’t, all your tabs will be converted to bookmarks when you upgrade. The transition is much smoother if you install the addon first.
Also, I’m sorry I’m a bit late–I meant to warn you a few days ago.
Hopefully there are fewer people who use this than used the Addons Bar or other pre-Australis features.