This old question is too outdated to be of any significance - it involves the old version of Opera, and the browser is now very different. So please don't flag this as duplicate.
Opera 20 has a bookmarks bar which can contain also folders. But I don't seem to find a convenient way of importing my bookmarks from Firefox while keeping all their structure.
I've discovered that drag and drop works for individual links but not for folders and that is useless for hundreds of bookmarks.