Australis displays at least 17 tabs before expanding into the tab-scroll view when full screen, which is more than I'd typically have open at a time anyway.
Tab-scoll, to me, makes a lot of sense as it prevents any confusion over the content of the tabs, especially when those tabs lack favicons: in Chrome, you simply get a blank page icon when the scroll bar overflows.
The only downside to Australis for me so far has been the removal of the "thin" address bars/small icon sets, there is no longer an option within Firefox to enable them, as far as I know.
http://i.imgur.com/8JIwdgh.jpg
Tab-scoll, to me, makes a lot of sense as it prevents any confusion over the content of the tabs, especially when those tabs lack favicons: in Chrome, you simply get a blank page icon when the scroll bar overflows.
The only downside to Australis for me so far has been the removal of the "thin" address bars/small icon sets, there is no longer an option within Firefox to enable them, as far as I know.