A state-of-the-art interface is a modern IMAP mail client.
Let me guess, Pine?
Explorer doesn't even have a split-pane mode that I can find
Just Control-Doubleclick a folder and it opens in a new Explorer window. From a little demonstration video that I saw, I can say that two Explorer windows are better than one split view Dolphin window.
Ask yourself; what can be accomplished with a cookie that can't be accomplished using alternative mechanisms.
Let's use URL rewriting. My friend shares a photo from their private album with me, I post a link to it on Twitter and the next thing I know half the world has my session id.
The end of labor is to gain leisure.