like one said: the search-bar functionality is gone like this. looks nice, but the workflow stumbles.
Why not integrate the url-bar into the search-field? Use a keyboard shortcut or "scroll search engines" to switch between the "search engine" url-bar and other, real search engines. Funny enough, if you add a history of search terms for every one of the search engines (yeah, give it some "forget" options), you could use the back and forth buttons not just for urls, but for search terms per engine, too. But that's just m 2 cents.