arrived earlier this autumn, and it gave us a taste of some other new features, like lightweight browser add-ons and some hardware acceleration features new to version 11. Those features have been refined and are included here along with the new tab tricks.

If you’d like the take the beta release for a spin head over to Opera’s download page.

Tab Stacking, the standout feature in this release, is ingeniously simple and works a little bit like the way you create folders of apps on the iPhone’s home screen. You group related tabs by dragging them on top of each other. Your “stack” then collapses down into a single tab. To access the tabs in a stack, you simply mouse over the group and it expands, or you can click the arrow to the right of the grouped tab, which has the same effect.

The idea of grouping tabs is nothing new. Firefox 4 will also introduce a new interface for grouping tabs when it is finalized in a few months.

Only a slim one or two percent of the desktop browser market uses Opera daily. Still, the company is known for building innovative user interfaces into its browsers ahead of its larger, more widely-used competitors. Things like mouse gestures, or the page that shows thumbnails of your favorite sites when opening a new tab were first introduced in Opera. So it’s a change of script to see the company in the position of playing catch-up to the big names when it comes to grouping tabs and supporting lightweight add-ons.

However, Firefox 4’s current implementation of grouping tabs together (also still in beta) suddenly looks awkward and primitive next to Opera’s take on the same idea. Opera’s approach is more elegant, and it plays on a behavior many users — those with iPhones or iPads — are already familiar with.

The best way to understand Tab Stacking is to see it in action:

Opera’s mouse gestures have been improved in this release, though there’s still not much support for gesture-based trackpads. In my testing, gestures like pinching zoomed in and out, but other options like three or four-finger swipes aren’t supported.

Also new in Opera 11 is a a visual interface that highlights mouse paths and makes it easier to understand and customize mouse gesture shortcuts. Check out Opera’s guide to mouse gestures for more details.

The beta release also sees the launch of a new website for publishing and searching Opera extensions. Thanks to Opera’s decision to base its extensions framework on the W3C Widget specification (which defines a “widget” as a downloadable and locally stored web application), it should be relatively easy to port existing Chrome and Safari extensions to Opera’s platform. So easy, in fact, that Opera reports developers are submitting between 10 and 20 new extensions each day and users have already downloaded some 500,000 add-ons.

Opera’s extensions framework also gains an automatic update system in this release, enabling add-on developers to push updates to users browsers. This means you’ll never need to worry about making sure you have the latest version of your favorite add-ons.

One thing you may not find in the new extensions store are Flash-blocking add-ons. Actually you probably will, but you don’t need them. Opera 11 can now be set to load plug-ins (like Flash or Silverlight) only on demand. Just head to the preferences menu, select the Advanced tab and then click Content. There, you’ll see a new option to only load plug-ins on demand. The feature is disabled by default.

Of course, all the new features would be less exciting if they slowed things down, but luckily they don’t. Opera hasn’t given any hard and fast numbers, but in our experience Opera 11 is faster than its predecessors and on par with Firefox 4 and Chrome 7.

Linux fans will be happy to hear that the platform has seen a bit of extra attention in this release. Opera claims that the beta is 15 to 20 percent faster on common benchmarks than Opera 10.63 for Linux.

Perhaps even more impressive, Opera 11 is actually 30 percent smaller than previous releases, saving you a bit of download time and disk space.

Other noteworthy features in the Opera beta include a revamped, simplified URL bar, which, like Google Chrome, dispenses with the “https://” bit at the front of URLs and highlights the security status of the current page. Unlike Chrome though, when you click inside the URL bar, Opera will reveal whether you’re connected using http or https.

Another trick borrowed from Google Chrome is support for Google search predictions. The feature works in both the search field and from the address bar when you start your query with the “g” shortcut.

With hardware acceleration, add-ons support and the innovative interface of Tab Stacking leading the way, Opera 11 is shaping up to be a great release both for Opera fans and those who use other browsers, which, if history is any guide, will soon be mimicking Opera’s lead.

This article originally appeared on Webmonkey.com, Wired’s site for all things web development, browsers, and web apps. Follow Webmonkey on Twitter.

More from Webmonkey:

• Opera’s Next Act: Add-ons, Hardware Acceleration, Android
• Opera 10.6: WebM Video, HTML5 and More Speed
• Chrome 8 Adds Google Instant to the URL Bar
• Happy Birthday Opera: The Innovative Web Browser Turns 15

Authors: Scott Gilbertson

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