Opera 15 looks really quite Chrome-like. For example, it has a unified address/search bar, browser settings are now in tab rather than dialog boxes, and there’s no status bar. Opera has also dropped support for the extension format for Opera 11 and 12 in favor of Chromium’s extension format. Which means, you can now install extensions from the vast Chrome repository. However, when you visit the Chrome web store you will notice that there is no “Add to” button on an extension page.
If you want to install an extension from Chrome Web Store in Opera 15, you need to install an Opera add-on first that was created specifically for the purpose. Go to Download Chrome Extension add-on page and install it. You should now see a new “web store” icon added to the Opera toolbar.
Now to install an extension from Chrome’s Web Store, visit the extension’s page you want to install and hit the newly added icon in the toolbar. The extension will be downloaded in the background, but Opera will block the installation as Web Store is not an approved source. You’re informed of this with a notification at the top:
Extension was disabled because it is from unknown source. Go to the Extensions Manager to enable it.
Hit OK, and open
opera://extensions page in the browser. On this page you will find the extension listed already but disabled. When you click on the Install button corresponding to it, you’ll see a list of permissions that the extension requires to function. Click install again to enable it in the browser.
Opera 15 only supports a subset of Chromium extension APIs, as well as its own Speed Dial APIs, so some extensions might not be compatible just yet. However on a positive note, you can now install extension from Chrome Web Store, official Opera add-ons, as well as from third party download sites. (via gHacks)