Mozilla Links has a nice short post on the recent theme changes that landed on the trunk, where main development for Firefox 4 occurs.

Similar to Opera, or Opera was similar to Firefox' concept art, who cares anyway, there is now a "Firefox" button (labeled Minefield due to being a nightly) that offers the basic menu functionality which is now hidden by default. The menu button itself has a layout of menu items which is based on a hotspot (thermal) image of user activity and should host the most important functionality. The loss of the menu bar (which can be re-enabled by the way) is traded for more vertical space, which is important since we mostly have more horizontal space these days due to widescreen displays.

Other well deserved changes include support for Aero glass, which is finally coming while since Vista this has been a pain in the butt for those who like esthetically pleasing Windows apps. The tab bar is now on-top, similar to Opera and Chrome, in which Alex Faaborg goes in-depth to explain the choice (once more, yes you can change this back).

As you can see some important puzzle pieces are in place for the first beta of Firefox 4 which should appear somewhere in the coming weeks. It looks like Firefox is finally making a serious effort to be "there" in the usability area once again.