Mozilla has competed the merge of Firefox 10 on to the Beta developmental channel on December 23, 2012.Existing Beta users can update via Firefox Button > Help > About Firefox. New users can download via the Firefox Future of Firefox site.

What’s New in Firefox Beta for Web Developers:

• Full Screen API: Developers can create Web applications that leverage the entire screen. The Full Screen API works with any HTML content, enabling developers to build entertaining and compelling Web video and game experiences. You can get more information in this blog post.
• Page Inspector: Page Inspector makes it fast and easy for developers to test the design, style, font, color and page positioning of their website. Developers can see the HTML and CSS rules applied to any selected page element. This makes it easy to navigate through different page elements while viewing the HTML document structure for the page.
• Style Inspector: Developers can use the Style Inspector to see the CSS properties applied to any selected page element and easily change the values to experiment with new looks. You can get more information in this blog post.
• CSS3 3D-Transforms: Developers can create two-dimensional elements that animate and transform into 3D using HTML5 without the need for third-party plugins. You can get more details in this blog post.
• Anti-aliasing for WebGL: Now 3D WebGL content will have edges that blend smoothly, especially with games and animations.
• Scratchpad with Orion Code Editor: The developer Scratchpad adds the Orion code editor, allowing developers to edit more than plain text. The Orion code editor provides syntax highlighting and other great features and makes it easier to write JavaScript.

What’s New in Firefox Beta for Users:

• Add-ons Compatible by Default: Firefox updates are smoother and easier because incompatible add-ons are automatically disabled and all other add-ons will default to compatible (except binary add-ons). We need your help testing the update process to make sure that incompatible add-ons are properly disabled. You can read more details in this blog post or file a bug.
• Enhanced Firefox Sync: Firefox Sync is enhanced with an easier setup process so you can pair your Android phone, tablet or any Firefox-enabled device without needing to be at your desktop computer.

Firefox 10 is scheduled for release on January 31st, 2012. For more information see Mozilla Future Releases Blog.