I made a new extension for Opera based on an extension for Safari by Deep Informational Technologies. Thank them for making the original available under an open license allowing me to make the Chromium port.
Click the Site Home toolbar button and you will be redirected to any website’s home page. It will consider the site’s domain name as its main page. Plain and simple.
The extension is no longer available for download, but you can still get the source code on GitHub.
Update (): Please note that I don’t intend to maintain this extension in the future as I kind of lost interest in Opera. The source code is available under a permissive MIT License for anyone interested in updating it in the future.