Sometimes I can select "Show Toolbar in Full Screen Mode" - Sometimes its greyed out. It's very annoying. I like full screen mode actually without all the tabs...but I think a better implementation would be to show the tabs when the mouse hits the edge of the top screen, and then dissapears when it hovers below.
Anyway, it's super annoying. It's greyed out, and the only way I know how to fix it, is to restart opera, and then I can select the "Show Toolbar in Full Screen Mode" again.