I've been using Opera for years, if I did need anything I'd use UserJS (Greasemonkey done properly, built-in). I have no extensions, and only two userJSs (youtube download, and gawker fix). I have adblocker and firebug as built in functions of the browser, I have custom searches instead of things like Tineye extension that I have on Chrome.
... what? Why in the world? If no browser had extensions I'd probably quit the web altogether.