Firefox 4 Beta 1 has officially been announced, with Mozilla hoping that its next generation browser can prevent rivals like Google Chrome and Apple's Safari from eating into its market.

The candidate build surfaced at the end of June, but the company has now formally rolled out Firefox 4 Beta 1 for testers.

Firefox 4 will bring a host of new features, and the first full beta release will showcase the biggest change, a big change to the user interface.

Top tabs

By default tabs will now be at the top of the browser – in a style reminiscent of Opera and Chrome, and will be joined by new features such as a revamped add-on manager, WebM HD video support and privacy improvements.

"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," blogged Mozilla.

"Once you download Firefox 4 Beta 1, you're part of our beta program and will receive regular updates as more features launch."

User experience

Mozilla explained that the decision to move the tabs was based on improving the user experience.

"If you are using a Windows PC, the most noticeable new feature will be the look of the browser.

"We 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 was replaced with a single Firefox button so you can get to the most used options with just one click. These changes will be coming soon for Mac and Linux."