Hi,

The people who answer questions here, for the most part, are other Firefox users volunteering their time (like me), not Mozilla employees or Firefox developers.

If you want to leave feedback for Firefox developers, you can go to the Firefox Help menu and select Submit Feedback... or use this link. Your feedback gets collected by a team of people who read it and gather data about the most common issues.

Update :

It isn't completely possible to use the Australis design with Firefox 57, but depending on what you want, you might be able to customize the UI to look more like the old one:

   This project: https://github.com/wilfredwee/photon-australis lets you have the old tab bar appearance back in Firefox 57.
   You can remove the space around the address bar by right-clicking on the spaces, and choosing "remove from toolbar".
   Is there something else specific you're looking to change? 

Here's a more comprehensive project which affects not only tabs but brings back the old "grid-style" options menu.

https://github.com/axydavid/FirefoxUI/blob/master/README.md

Note the Black Theme can be changed in Optimize it is only the example.

Please let us know if this solved your issue or if need further assistance.

Perhaps this image, taken after upgrading to the previous, and more tolerable, version of Firefox, will explain my issues more. This is the work of multiple addons to fix all of the attempts by Mozilla to turn Firefox into Chrome (which I would have just downloaded in the first place, if that's the browser I wanted).