Very soon, the first build of Opera 11 will be released, and with it will come the long-awaited support for browser extensions.

Yesterday at Up North Web, Opera Software’s global press day in Oslo, Norway, it was confirmed that Opera 11 will support browser extensions, the plug-ins that users can incrementally add to their browser to customize the experience. All of Opera’s competitors: Internet Explorer, Firefox, Chrome, and now Safari, each offer their own extension architecture already.

Opera’s extension platform will be based on the W3C Widget specification and developers will be able to build them in Web standards such as HTML5, CSS, and JavaScript. The W3C’s spec uses PKWare’s Zip specification as the archive format, XML as a configuration document format, and “a series of steps that runtimes follow when processing and verifying various aspects of a package.” The most recent draft of this standard was completed on October 5.

Extensions will not be available until Opera 11 is released, but it will be available in the earliest alphas of the browser. It is unclear when the first build will be released, but it is certain to be quite soon.

Today, the Opera desktop team revealed that build 9071 will be the last Opera 10.70 version, and the very next release will be the first version of Opera 11.

In this alpha, the extensions platform will support injectable JavaScript, callouts, UI items, as well as a basic Tabs and Windows APIs so developers may begin building and testing their projects.