Mozilla has released Beta 2 of Firefox 4, which is now available in 24 languages.

The update includes many changes, including apps tab feature.

“There are some websites you visit many times throughout your day, such as your email, social networks, music or game sites. Now you can turn the websites you use most into App Tabs to easily find the ones you need” said a release from Mozilla.

Mac users now receive the new interface that was delivered to Windows users in Beta 1, and puts tabs on top by default.

There is also more support for CSS3 transitions, retained layers allowing for faster scrolling on complex websites, and changes to the XPCOM framework reducing the browser start up time.

A full list of changes can be read in the release notes. Firefox 4 Beta 2 can be downloaded from the Firefox Beta website.

Mozilla have released Firefox 4 Beta 1 to the public, after final beta 1 builds started to appear last week.

Firefox 4 has many changes over 3.6, and is based on Gecko 2.0 rendering engine. New in Firefox 4 include:

• Tabs on top for Windows by default  (Mac and Linux changes coming later)
• Menu bar replaced by Firefox button for Windows Vista and Windows 7 users
• New add-ons manager
• CSS transitions
• Native HD HTML5 WebM video support

A full list of changes can be found in the release notes. Firefox users can download Firefox 4 Beta 1 from the Firefox Beta website.

No change log has yet been released, and Mozilla will not announce the release until a final Beta release is ready. There are currently two bugs blocking build 2, which are expected to be fixed shortly. Currently the release is available for Windows, Mac, and Linux, with native 64-bit builds for Mac and Linux users.

Would-be-testers are warned that while more stable than the alpha releases, this build still has a lot of work to be done before it is ready to be used by the masses. As a result, some of your plugins may not work with this release.

More information on Firefox Beta 1′s release can be seen on the MozillaWiki. Firefox 4 Beta 1 Build 1 can be downloaded from the Mozilla FTP server.

Early builds of Firefox 4 are starting to show the browser new interface.

Part of the revamp includes moving tabs above the address bar by default, which isn’t something everyone is happy about. Thankfully, this can be changed easily by the user.

“This is a preference that users can change by right clicking on any of their toolbars.  Moving the default tab position is obviously a significant and to some extent controversial change to the Firefox UI, which is why we made the video above to help explain our rationale” explains Alex Faaborg, User Experience Design at Mozilla.

Firefox 4 Beta’s are expected in the next few weeks, with a final release before the end of 2010.

WebM support is included in Windows, Mac, and Linux Firefox nightly builds. Previously, WebM had been made available by special builds that were announced with the release of the WebM format.

Firefox Programmer Chirs Pearce has posted details on his blog for users wanting to build the browser themselves.

Eager testers can download Firefox 4 Alpha from the Firefox nightlies. Firefox 4 final is expected before the end of the year.

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.

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.

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.