Wary of the looming presence of Google Chrome and Apple Safari, Mozilla has released the first beta of its Firefox 4.0 web browser. The candidate build surfaced at the end of June, but the company has now formally rolled out Firefox 4 Beta 1 for testers.

From the sounds of it, Firefox 4 won’t just be a minor clean-up operation either, Mozilla seems determined not to shed users Explorer-style. In turn, the new significant features included in the Firefox 4.0 beta will be:

* Add-ons Manager: “More space to efficiently manage your favourite add-ons, plug-ins and themes.”

* HD Video: “The future WebM format is supported and promises HD-quality hardware accelerated HTML5 video on the web.”

* HTML5 Support: “Better HTML parsing, support for HTML5 form controls and also runs the latest web apps based on HTML5 such as Google’s Gmail and Yahoo’s Mail interface for the mobile phones.”

* Full WebGL support for in-browser 3D rendering.

As for the big change to the user interface – well a blog from Mozilla reveals that, if you are using a Windows PC, it’s “moved the tabs to the top to make it easier to focus on the web content and easier to control the tools in your web browser”.

Also, if you have Windows 7 or Windows Vista the menu-bar has been replaced “with a single Firefox button so you can get to the most used options with just one click”. The blog adds that these changes will be coming soon for Mac and Linux.

“Firefox 4 Beta 1 includes dozens of major features and improvements– by testing them early we’ll be able to respond to your feedback for future versions of Firefox,” the company continued, “Once you download Firefox 4 Beta 1, you’re part of our beta program and will receive regular updates as more features launch.”