That wouldn't make any sense anyway. You'd have to keep separate cookies per tab, but tabs have no identification for persistence. So you open two gmail accou

That wouldn't make any sense anyway. You'd have to keep separate cookies per tab, but tabs have no identification for persistence. So you open two gmail accounts, one in each tab. Close them both. Open a new gmail tab, which account will you be in? The logical conclusion is that, in your scenario there are no cookies written to disk. With profiles, each profile has its own set of cookies and you are deliberate with respect to the profile you are in. Cookie behavior is well defined, predictable.