Some browsers do that in full-screen mode now. By the way, in Opera you can configure browser that way so toolbars will auto-hide. You can assign shortcut or a gesture to them. Hovering isn't a good idea because it will eaither have to move the page (which is distracting and annoying when you do it on accident) or cover the page (which could block some content). So having it on gesture and/or shortuct would be the best way in my opinion. If you want the toolbarless experience. (I personally don't)