Classic Theme Restorer has been designed to bring back features and designs that Mozilla removed when it launched the Australis interface back with Firefox 29.
The extension has evolved over time and it does more than changing rounded to squared tabs. In fact, it always did more than that but its author has added new features on a constant basis that may make it interesting even if you like the Australis interface and the changes that came along with it.
This guide looks at ten reasons, or features if you want, that
Classic Theme Restorer offers that make it an interesting add-on that Firefox users should take for a trial ride.
Worst thing that happens is that you don't need what it offers, and that is easily fixed by uninstalling it again from the browser.