It is still frustrating that a bunch of plug-ins appear to have been disrupted because of removing the add-on/status bar, though. Not everything has moved to the new location automatically, and it's not immediately obvious how to get some of them back.
I just installed JS Switch on Nightly and clicked the Menu(burger) icon, then Customize, and was able to drag the JS Switch button into my toolbar.
(This does not address that it's crappy that icons that were in the addon bar don't, say, automatically get put into the toolbar or trigger a message notifying you how to get them back or anything, but oh well. EDIT: According to another reply this may not be the case with all addons, seems like some automagically get moved.)
I develop a Firefox add-on. In our experience, the transition to Australis was pretty smooth. Our add-on bar icon was automatically moved to the toolbar without any changes on our part, although we ended up changing the icon to better match the Australis UI. The transition might not be perfect for all methods of overlaying the add-on bar, but I think the folks at Mozilla are doing the best they can.
I don't think Mozilla should be holding back functionality to avoid breaking extensions. If an add-on is actively maintained, then the developer will update it, and if the add-on is not actively maintained, then it's going to have to break someday.
I don't think Mozilla should be holding back functionality to avoid breaking extensions.
I respectfully disagree. Extensions are the USP for Firefox, and IMHO breaking compatibility should be considered a serious issue and not something to be done lightly. (See also: all the hate when they switched to doing six-weekly updates and it kept disabling extensions every time for months afterwards.)
In any case, there was no pressing need to remove the add-on/status bar. Arbitrary rearrangement of UIs is generally bad for usability. Ditto for major things like moving tabs (for anyone who isn't using an enhanced tab plug-in anyway) and the burger menu (which is now a tiny area right underneath the close window button, and appears to be completely inaccessible by keyboard).
Some things seem to have moved automatically up to the toolbar. If that's happened, you'll now find them at the top-right of your window, between the search box and the burger menu.
I'm not sure what is supposed to happen with plug-ins that actually used the status bar for more comprehensive status information, such as the system you illustrated. You could check whether your (Burger)->Customize screen gives you anything you can dump on a toolbar somewhere as 'Osmose suggested, but since it appears you can only have one row of toolbar contents, the new model just seems to be broken for your purposes. :-(
It is still frustrating that a bunch of plug-ins appear to have been disrupted because of removing the add-on/status bar, though. Not everything has moved to the new location automatically, and it's not immediately obvious how to get some of them back.