I use GNOME shell but I have my buttons on the left because I prefer it that way. Since Opera uses it's own title bar when maximized, it puts the close button on the right for some reason. Aside from that, it's pretty nauseating having the titlebar disappear for this one application and no others, as well as not being able to grab the very top bar (since the tabs are there) to minimize or go into windowed mode, forcing you to grab that tiny space on the right. 9 times out of 10 I end up pulling a tab off and making a new window. I like opera but I'd at least like it to be able to have buttons on the same side as the rest of my OS or just use titlebars like in windowed mode. You can have titlebars in KDE why not in GNOME?