Sadly, it looks like this addon is not being maintained. On top of it, it does not seem like Opera's API provides workspace information to differentiate tabs opened in other workspaces. 😞
@jb909: @jb909: Hello. I'm glad that I was able to interest you in this extension, and I'm sorry that it didn't work. YouTube made changes to the site, and an update was required.
The latest version has been sent for moderation. You can test it in Opera developer version
Great extension! The only thing it lacks is some settings for the window itself, like I would want to make it wider so it can show more text in a line.