When it comes to modern browser design, it seems, all roads lead to Chrome. Mozilla developer Jared Wein has posted an early build of Firefox featuring the revamped Australis user-interface design, and the build looks awfully similar to Google's browser. Here's the new nightly rendering TR:
...and, just for reference, here's the latest version of Chrome with the same tab layout:
The new Firefox design seems to blend background tabs completely into the window frame—unless, that is, the mouse cursor is hovering over them (as it is on the left-most tab in that screenshot). Still, the tabs-on-top layout with curved tabs is clearly inspired by Google's design, which has stayed largely unchanged since the first public Chrome beta came out four years ago.
Judged on its own, though, I'd say the new Firefox "Australis" interface style does look good, and I look forward to Mozilla polishing it up and integrating it in main Firefox releases. I think the clean, smooth lines work better than the more rigid, rectangular ones of the current design. There's more where that came from, too.