Opera released the Alpha version of Opera 11, the version which supports extensions.
Warning: This is a test version.
Because this is an alpha version, it is not feature complete—there are still many more features to come. Use it with caution, ensuring that your current Opera installation and any other important data are backed up before installing this version.
Features
Introducing Opera extensions
Increasing browsing performance
Enhancing browser features
Supporting the latest in web technologies like HTML5 server-sent events and websockets.
Read more and download