Nightly releases of Firefox 4 now include Aero Glass for Windows Vista and Windows 7 users, with the feature still a work in progress.

“The feature was available first in early April but pulled back soon after to iron some important bugs” noted Mozilla Links Percy Cabello.

The above screenshot also showcases the ability to hide the menu bar, and move the tab bar above the location bar.

Keen users can test the new interface by downloading a copy of the latest Firefox nightly.

Mozilla has given a presentation discussing Firefox.Next, now officially known as Firefox 4, which bypasses the often talked about Firefox 3.7 version number.

New features set to make an appearance in the browser include:

• Speed – it will be “super-duper fast”
• Power – it will support “HTML 5 and beyond”
• Empowerment – users will be allowed to fully control their browser, its data, and their web experience
• Completely re-vamped user interface allowing layout customization and less chrome
• Improved stability and security
• Ability to install add-ons without restarting browser
• Better tools for developers
• 64-bit support
• Hardware acceleration
• Multitouch support

Currently, a Firefox 4 Beta is expected in June next month, with a possible final release planned for November, or Janurary if development slips past the November time-frame.

The full 50 minute presentation can be downloaded or watched online.