Click the link, click install. That's about as tedious as it gets. I've actually been using fewer addons as time goes on and the Classic Theme Restorer addon has some additional UI tweaks that I find interesting.

That said, I generally use two Firefox profiles: One for general browsing, one for documentation. The former is configured to use Australis more or less as packaged while the latter is configured to appear as closely as possible to classical Firefox (minus the FF button). Although there are some things I don't especially like about Australis, it's grown on me, and I'm someone who likes his tabs below the address bar. Thus, as someone who's been using both, I can't help myself from thinking that you're either not giving the new UI a fair wrap or you're being unnecessarily harsh. Some of your earlier comments in this thread strongly point toward the latter, but I suspect I'm just reading too far into your apparent disappointment. Or your disappointment is coloring your opinion more than you might realize. The point is that there are solutions to rectify what you perceive as significant drawbacks in the direction of Firefox's development.

> or to fix up functionality that has been broken or made worse.

To be honest, the only glaring issue I've found with FF29 is the rather horrid behavior of the print dialog. I like the direction it's going, generally, but under KDE, it doesn't allow printing a selection of text unless I re-enable the menu bar and print from there (maybe this works under Windows, I haven't tried). Otherwise, I can't think of any other issues that have been "broken or made worse." Compared to Chromium with 50+ tabs open, Firefox is exceptionally light on system resources, and I've since switched my browsing habits to use FF instead. I'm glad I did. It works well for me.