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.

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.