First Firefox 4 pre-release build available for download

The Mozilla Foundation has given developers their first glimpse of Firefox 4, with the first pre-release build of the browser now available on the nightly builds page.

Firefox 4 is pencilled in for full release in November, and while an official beta is only expected sometime in mid-July, the pre-release build officially titled Firefox-4.0b2pre but dubbed "Minefield" by Mozilla developers offers a preview of what the new browser has in store.

Thus far, details on Mozilla's fourth-generation browser have been limited to what was shown off in a presentation by Firefox director Mike Beltzner early last month.

At the time, Beltzner promised Firefox 4 would be "super-duper" fast, and would come with a simplified user interface, full touchscreen and 64-bit support as well as HTML 5 integration.

"The simpler it looks, the faster it will seem," Beltzner said at the time. "We're looking at making our interface faster just by changing the way it looks."

One such change mentioned by Beltzner and present in the first pre-release build is that the default position of tabs has moved to the top of the screen, following in the footsteps of Chrome and Opera (though there is the option to revert to the current layout).

The typical menu structure at the top of the screen has also been overhauled, and is now dominated by an Apps button to easily launch commonly used services such as Gmail.

Also new in Firefox 4 is JaegerMonkey, a JavaScript engine extension that works with the existing TraceMonkey and according to Mozilla, delivers improved speed. As expected, support for Google's recently certified WebM open-source video format is also included.

One feature yet to materialise is the promised JetPack SDK, which Mozilla claims will make it easier for developers to create plug-ins using HTML, JavaScript and CSS, and removing the need for users to restart the browser when new add-ons are installed. For now, however, the add-on page simply displays a message saying: "This page isn't done; lots more improvements coming soon!"

Firefox principal designer Alex Faaborg has put together a demo video showcasing the browser's new features and explaining the rationale behind moving the tabs to the top of the page, while the pre-release build itself can be downloaded from the Firefox Nightly Builds page.