A feature that allowed you to save and restore browing sessions would be great. It'd also be nice if it could automatically save sessions at user-defined intervals—sometimes one closes more than one window accidentally, or launches and then relaunches the browser, disabling the "Reopen All Windows from Last Session" option.
I realize that there are extensions for this (though the ones I've tired are broken per my bug report), but a built-in feature would allow the names and the positions of the windows to be preserved.