If you like Opera Dragonfly, as I do, you may have stumbled upon a small annoyance: if Opera is configured to start with the previous window, if you use Dragonfly in a separate window - maybe because you use a dual screen config - if you happen to close the main Opera window with Dragonfly still open, and close Dragonfly afterwards, then you will notice that Opera complies with your choices: when you restart it, it restarts with the main browsing window closed and Dragonfly opened.
At this stage, closing Dragonfly won't help, because Opera will faithfully restore it at every launch. Annoying. Luckily, there is a very simple workaround if you find yourself in that situation...
Drop the the command line and run:
opera -nowin
This will open Opera without using the saved windows configuration, in this case without Dragonfly, but with a normal main window. If you close it again at this point, everything will be normal from then on.