Wrong forum, moved to the add-ons forum. But if you're talking about hosting it yourself, that is probably not allowed - for security reasons the browser will only download extensions from Opera's add-ons site.
If it's avaiable for chrome, you can add it to Opera using this extension: Install Chrome Extensions. Also I see that it requires a desktop/pc version as well, make sure you have the program installed on your machine. That could be another reason why Chrome opened when you tried to add it.