Editors' note: This post originally stated that the Opera 11 beta was not yet available for Linux. In fact, Opera 11 beta 1 for Linux is available for download here.

Opera may be getting most of its attention these days from its mobile browsers, but that doesn't mean that the company is ignoring its desktop browser. The first beta for Opera 11 introduces a long-missing extensions API in a lightweight profile similar to those that run on WebKit-powered browsers like Chrome and Safari.

Available for Windows, Mac, and Linux, Opera 11 beta 1 debuts other minor but useful changes. The most noticeable of these is tab stacks, a tab grouping mechanism similar in concept to Firefox's Panorama but completely based in the tab bar. To use it, drag one tab on top of another. The bottom tab will disappear and an arrow will appear to the right of the tab. Click it and the tabs in the stack will slide out to one side. To break up a stack, drag a tab off the stack. Mouse over the stack to see previews for all the tabs in the stack.

Another tweak made to tabs is that when you pin a tab, it will automatically jump to the left side of the tab bar. The personal bar has been replaced by a bookmarks bar, both pulling the browser into parity with the competition and making bookmarks accessible with one click.

Plug-ins such as Adobe Flash can now be set to load on-demand, via a check box under the Content section in Preferences. This will allows pages to load content faster and minimize somewhat third-party-plug-in-based exploits, and was impressively smooth in its implementation.

Opera's extension network will look and feel familiar to anybody who's used extensions in the WebKit-based Chrome and Safari. (Credit: Screenshot by Seth Rosenblatt/CNET)

Opera claims the tweak can improve performance up to 30 percent, and that the browser's performance in general has been improved. Opera says that Opera 11 beta 1 is 15 percent to 20 percent faster than Opera 10.63 on Linux, and that the browser size on disk has been reduced by almost one-third.

Opera's security badge system marking sites as verified safe has received an overhaul, too. Click on the gray "Web" globe icon to the left of the URL bar to check a site's status. Getting information returned was quick with some sites and slow to stalled with others in the beta. Other color-coded badges include yellow for "secure" and green for "trusted." Opera's take on the feature is interesting because it provides quick links for reporting a site as fraud or malware. When browsing with Opera Turbo on, the badge will display estimated data savings.

Finally, the mouse gestures tutorial has been given a visual refresh, making it easier to learn them.

Opera's extensions gallery has 131 extensions at the time of writing, which sounds tiny except for the fact that extension support has been available only in a limited alpha release for the past month and appears to be mostly sourced from Opera's internal development team. Now that the feature is ready for a wider release with the beta, expect the number of user-contributed add-ons to jump.

Tab stacks group your tabs using drag-and-drop and are visible via mouse-over previews, so they feel like an extension of your current tab-navigating habits. (Credit: Screenshot by Seth Rosenblatt/CNET)

Much like the WebKit-based add-on network, Opera's extensions install as buttons to the right of the search bar and auto-update. Though they might seem to some users to be in conflict with the browser's existing widget network, Opera spokesman Thomas Ford says that's not the case. "Widgets are stand-alone Web-based applications. They are meant to showcase the browser as an application platform. To that end, widgets work across PCs, phones, TVs, and other environments. Extensions are really there to let you tweak and customize your browser experience."