Mozilla just released Firefox 4, the next generation of its popular Internet browser. This new version is not just significantly faster than Firefox 3, but it also features a new, highly streamlined interface and a number of new tools that should make Firefox 4 even more popular among power users.

There are lots of new features in the new version of Mozilla’s browser (plugin isolation on all platforms, support for modern web standards like HTML5, new security and privacy features, etc.), but here are the key new features of Firefox 4:

Streamlined Interface:

Interface ff4

In Firefox 4, Mozilla’s designers worked to keep distractions to a minimum and reduce the interface clutter in favor of providing more screen estate for the Web itself.

Gone, for example, is the menu bar in the Windows version. Instead, similar to Chrome and Internet Explorer, all the options are now available in one menu and the tabs have moved up to the top of the window. Bookmarking, too, has become easier and faster and just takes one click now.

This doesn’t mean that Firefox 4 was dumbed down, though. A lot of cool functionality for power users is just a bit hidden but easily available. You can use the URL bar to switch between tabs, for example.

Speed:

According to Mozilla, Firefox 4 is six times faster than version 3. To a large degree, this is due to JaegerMonkey, the optimized JavaScript engine that allows web apps like Gmail to run much faster than ever before.

As Mozilla’s director of Firefox Jonathan Nightingale told me last week, the traditional SunSpider benchmark, which was long the gold standard for measuring JavaScript performance, is slowly coming to the end of its usefulness. The difference between browsers in this benchmark is now often measured in milliseconds and, as Nightingale put it, “to do better, you now have to play to the test.” Other benchmarks like Mozilla’s own Kraken project or Facebook’s JSGameBench now provide better real-world guidance for how well browsers are performing.

That said, though, I ran both the SunSpider and Kraken benchmark on Firefox 4 and compared it to the latest developer version of Chrome (11.0.696.16). On average (after three test runs on a Mac) Firefox 4 easily beat Chrome. (Kraken: 4211.7ms vs. 4963.5ms; SunSpider: 189.2ms vs. 212.5ms).

Benchmarks can only convey so much about how fast the browser feels, and most users won’t notice any significant differences between most modern browsers. Firefox 4 does feel significantly faster than any earlier version, though, and I can’t help but think that it also feels faster than Chrome now.

Firefox Sync:

Most of us now work on¬†multiple computers and Internet-connected devices every day, but it’s still surprisingly hard to keep bookmarks between these machines in sync. With Firefox Sync (formerly known as Weave), you can now easily keep all these machines in sync. All you have to do is type in your password (generated by Firefox) and Mozilla will keep your bookmarks in sync. Syncing to mobile versions of Firefox is coming soon, too.

It’s worth noting that Google Chrome offers a similar feature, too.

App Tabs:

App tabs ff4

App tabs allow you to, as Mozilla puts it, “give a permanent home to frequently visited sites like Web mail, Twitter, Pandora or Flickr.” Your apps then live in small tabs on the left side of your tab bar.

These app tabs will also alert you when something has changed in the web app (like a newly arrived email). This doesn’t work perfectly for all apps, though. Firefox watched for the site’s title to change, which most web mail providers do, but most other sites don’t.

I prefer Mozilla’s implementation of this feature over Chrome’s, because it defaults to loading all the links you click on in the app tab in a new tab.

If you become a regular user of app tabs, also consider installing the Easy App Tabs plugin, which allows you to turn a regular tab into an app tab by simply double-clicking on any tab.

Installing Plugins Without Restart

Yes, other browser developers already offer this (and didn’t spend close to two years developing their software), but for Firefox’s power users, this is a major update. Developers have to support this feature, so not every add-on will install without restarts just yet, but there are already quite a few out there that do.

As Nightingale told me, 40% of Firefox users today have installed add-ons. Today, close to 80% of these add-ons are compatible with Firefox 4 and more compatible versions are coming online every day. The new built-in add-on manager also makes finding and installing interesting extensions a lot faster and easier.

Bonus: Panorama

Ff4 panorama

Here is another feature mainly geared towards power users that stays out of the way if you don’t want to use it. Panorama allows you to visually organize your tabs into groups. You can, for example, open up a new group for the research you are doing and another one for your web mail. The two stay separate from each other. I know many people who love this feature, which made me include it here, but it’s not ideal for how I use the browser. Give it a try, though – it might just save you a lot of trouble and enhance your browsing experience.