I'm a bit late reporting this one, but Mozilla have released the first beta of Firefox 4. With this new version comes several noticeable changes. The most obvious change is one which is only present in Windows as of yet, but is a change which moves Firefox's UX closer to that of Google Chrome. The tabs no longer appear underneath the address bar, but above.
Along with this change, in Windows 7 you also get a "Firefox button" which is a replacement of the menu bar - thus further reducing the real estate required by browser elements. The Awesomebar has also been renamed the "Smart Location Bar" and allows users to search for open tabs and to switch to them easily. The stop and reload buttons have also been merged into a single button - again similar to Google Chrome.
The crash protection we saw added for plugins in version 3.6.6 has been expanded upon and improved in Firefox 4.
Support has also been added for WebM (HD HTML 5 video format), WebGL (OpenGL-like standard for using 3D with the HTML 5 canvas tag), and further improvements to it's support for HTML 5.
