Native 64-bit builds of Firefox 4 Alpha for Windows are now appearing in the Firefox Nightly builds, and are expected to be released simultaneously when Firefox 4 ships.

Mac and Linux users have had 64-bit builds since early April, but there is still limited plug-in support, with most plug-ins falling back to 32-bit.

“This is still just a very very very early experimental build” noted Mozilla’s John O’Duinn. This means the browser may not behave as expected, and testers are advised to proceed with caution.

Eager testers can download 64-bit versions form the Firefox Nightly repository.

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 Developer Rob Cambell has revealed that Firefox 4 is recieving a new DOM inspector, similar to what is found in other browsers, after it was removed from Firefox 3.

Currently, Firefox web developers use the Firebug add-on to achieve the same effect. Cambell has stated Mozilla is not out to “kill” the Firebug add-on, but to merely suplement it.

“Now every browser ships with a set of development tools. We didn’t feel that [the original] DOM Inspector was the right tool to include in the browser” wrote Cambell.

Early Firefox 4 builds that include the new, unfinished DOM inspector are available for download.

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.

Along with the customisable tab bar, Firefox 4 also looks set to gain a new add-on manager, which is currently receiving a major overhaul.

The new add-on manager works in a browser tab, removing the need for a separate window completely. Along with the standard options for managing extensions, themes, and plugins is the ability to manage both installed languages and search engines.

Currently it is still very much a work in progress, with not all functions working as intended, with  icons and the interface still not final. Other features are still yet to be included, such as silent extension updates.

The new add-on manager is expected to start appearing in nightly builds of Firefox 4 soon.

Latest nightly builds of Firefox include a new customisable tab bar in the browser.

New builds allow buttons in tabs to be removed, saving valuable screen real estate for heavy tab users.

Previously this has been possible with third party add-ons, or by modifying the browsers own CSS files.

The tabs in this build also appear to be more rounded, as has been apparent in early interface mock ups for Firefox 4.

This is only the start of changes, with tab animations and aero glass still on their way for the upcoming browser.

Eager testers can view the new tab bar in action by downloading the latest nightly builds from the Mozilla FTP server.

Mozilla is hard at work on the next version of Firefox, and the latest alpha builds include out-of-process support for plugins.

“Plugins such as Flash and Silverlight run in a separate process from the browser. If a plugin crashes it will not crash the browser, and unresponsive plugins are automatically restarted” said an announcement from Mozilla.

Currently, out-of-process support is only available on Windows and Linux versions, with Mac support still under development. This is only the first step, with each tab also expected to be moved to it’s own process in time, much like rivals Internet Explorer and Chrome have already done.

You can download the new test version of Firefox from the Mozilla Developer News Blog.

Mozilla’s Stephen Horlander has been hard at work, working on tab animations for the next version of Firefox, Firefox 4.0. The aim is to improve the user experience.

“One area that animation would be very beneficial is with tab interactions. Specifically moving/arranging tabs on the tab strip, closing/opening tabs and tearing off tabs into new windows. Presently the feedback here isn’t as good or as elegant as it could be” said Horlander.

“Some of the goals for animation are to make browsing feel faster, adding visual affordances that makes tasks more understandable and to make the browser more visually appealing. There is much more detail on the Wiki articles linked above. My goal was to quickly demo how this would actually look and feel because still images and wireframes can only convey so much.”

Below is am image preview of what it might look like when opening a new tab.

Video’s of the preview tab animations can be found in Horlander’s blog post.

Mozilla contributor Stephen Horlander is still hard at work, sharing his ideas for a revamped Windows 7 theme for Firefox 4.0.

According to Horlander, the expected Firefox facelift is now solely expected in Firefox 4, and not gradually through Firefox 3.7 and Firefox 4.0.

In this revision, the Application button (marked #1 on the mockup above) has been reworked to incorporate the new Windows 7 single button menus, already present in Paint and Wordpad on Windows 7.

Work has also been done on the toolbar and location bar.

More mockups and information can be found on Horlanders blog post.

Current Firefox users can download the Strata40 Firefox Theme, which gives the browser a similar appearance.

Stephen Horlander, a Visual Designer for Firefox, has revealed some Firefox 3.7 and Firefox 4 mock-up designs for Mac computers.

The designs are based on feedback and comments left about the firm user interface direction for Firefox 3.7 and 4 designs. Below are possible Firefox 3.7 and 4 interfaces for Mac.

More details, variations and information on these designs can be found on Stephen Horlander blog post.