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.
Introducing Opera extensions
A selection of add-ons can be chosen from our new extensions catalog. With Opera 11 alpha running, you can install extensions by just clicking on them. A small install window will appear. Click “Install”, and you are done. If you have an extension file stored on your computer, it can also be installed by dragging and dropping it into the Opera window.
More about extensions »
What does an extension look like? Some extensions have user interface elements, but not all do. For example, an extension can add a button next to the Google search field and show a pop-up menu when clicked. Other extensions do not have user interfaces at all but run in the background.
Once installed, managing extensions is a breeze. The extensions management window lets you easily uninstall and disable current extensions. Soon, we will add support for auto-updating extensions so that there are no worries about running old versions.
Download Opera 11 alpha for ubuntu
You can download deb packages from here
You can install this by double clicking on it.
You can install extensions from here
Check more details about opera alpha 11 from here