Ctrl-f in Opera bringing up a dialog is not very elegant, as it fills up the screen. Using "." or "," is not very convenient either, as it does not work if you are inside a text field (you'd have to press F9 first). Apart from that, it's a different key than Firefox.
Type "opera:config" in the address bar, "Show all", activate "Use Integrated Search" and "Save". Make sure that "Find in page" is available in search.ini.
Because every time I installed Opera, I spent another hour searching for how to enable this option. Groups Google only reveals that there was an option "Edit > Inline find" in the menu a long time ago that activated this feature.Contact information/Impressum