Mozilla is officially releasing Firefox 4 on Tuesday, but we managed to get our mitts on a copy a day early and poked around to see what you can expect from the latest and greatest version. Will version 4 manage to top the eight million downloads in only 24 hours from the last major release?

While public betas and even a release candidate or two have been hanging around for a while, it’s always an exciting time when a favored browser finally gets an official new release. That’s exactly what Mozilla is doing come Tuesday, March 22 with Firefox 4, the latest major version of the company’s ever-expandable browser for the Mac, Windows and Linux.

Firefox 4 is largely an under-the-hood release, bringing what Mozilla claims are “huge performance enhancements” over previous versions -- as much as six times faster than Firefox 3.6.12 when using the V8 Benchmark, version 6. The speed improvements come from the company’s brand-new JägerMonkey JavaScript engine, which not only boosts page loading but also app start-up time as well.

Seasoned Firefox users may be taken aback upon first opening Firefox 4 -- the main window now looks more like Google’s Chrome browser than the previous Firefox 3.5, with tabs above the URL and search fields. Mozilla claims this placement gives tabs “top visual priority for more efficient and intuitive browsing,” but it will no doubt take a little getting used to for veteran Firefoxers.

Other features getting a spotlight with Firefox 4 include Firefox Sync, which helps users keep your settings, passwords, bookmarks, history, open tabs and other customizations synchronized across multiple devices. Tabs can now be managed in groups to better organize your browsing experience, and you can even name groups to keep them straight.

Add-ons have always been a key advantage of Firefox, but the latest version adds a slick new Add-ons Manager which opens in a tab to keep the activity in your browser rather than a separate window. From the Add-ons Manager, you can quickly search for and add new add-ons, manipulate your existing extensions, change your appearance and manage your plugins, all from one central location.

The rest of Firefox 4’s superpowers are the kind users don’t see but will certainly feel in everyday use. Under the hood improvements include support for Google’s controversial WebM format, full OpenGL hardware acceleration on the Mac by default, CSS3 page styles including Transitions and Transformations, OpenType fonts and a new HTML5 parser with full support for web video, audio, drag & drop and file handling.

Perhaps the most welcome improved feature of Firefox 4 is crash protection. While the browser has always been quite good about recovering from the occasional crash and getting you right back where you were, the new version promises to bring the uninterrupted browsing from Windows and Linux to the Mac at long last -- “when there is a crash in the Adobe Flash, Apple QuickTime or Microsoft Silverlight plugins,” Mozilla cheekily explains.

The real question is: Should you switch from Apple’s Safari 5 or Google’s Chrome and give Firefox 4 a run on your Mac? In the short time we’ve poked around with it on Monday, we’d say it’s definitely worth a look -- Chrome users in particular will probably feel right at home, although both Chrome and Safari are ultimately a bit sleeker thanks to their underlying WebKit origins. And hey, the price is right at absolutely free!

If you’re the super-impatient type like we are, you can even jump the gun and get Firefox 4 today -- the full version is now available from Mozilla’s FTP servers, although the links won’t go live on the company’s website until Tuesday. Props to Download Squad for the direct links to the Mac OS X, Windows and Linux versions!

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