Cookie closure / chroot / universe / "separated cookies"

Lately I have become more worried about websites tracking my behavior across the web. For example, sites can (could?) embed Amazon banner ads that greet me with my name (which is a little bit creepy), if I have logged into Amazon. Or they embed Youtube video clips, or Facebook "like" buttons.

If I have logged in into those services, Each time the remote site gets to know that it is me specifically that is visiting the page. Combine that with what e.g. Facebook knows about me, It's a bit scary to think about what they know about me and my habits.

Private tabs and windows help a bit. If I open Facebook in a private tab, I can leave it on the background and If I come across a "like" button inside my non-private session and press it, Facebook will ask me to log in, because I'm logged in in the private tab, not in the non-private one.

Private tabs have their usability drawbacks, though: If I close one, I cannot reopen it with Ctrl-Z. They don't remember my visited sites, I can't block new content and I can't set site preferences, for example.

I'd like to extend this private/non-private model, that is in a way somewhere in between the two:

Tabs could have their own "cookie universe" that know nothing of other "universes." Each universe could contain multiple tabs, or even windows. So, you could have one universe where you're logged in to Facebook, another where you're logged in to Youtube and yet another where you're logged in Amazon. You could reopen closed tabs, do anything you currently do in your normal browsing session, search your browsing history, see what links you've visited etc.

Your "normal" session would be as it is now, this would be the default.

If you wanted to, you could "open a new universe", call it "the one where I'm logged into Facebook" and open Facebook there. If you visit some page with a "like" button in you "default universe", Facebook would ask you to log in. From the page context menu, you could "Open in... the one where I'm logged into Facebook" (similarly to how you can now click Open With... Internet Explorer) , and it would open the current page in the universe where that like button would actually share it immediately.

Additionally, the universes could remain even after you close all tabs in them and between browser restarts.

I guess you could emulate at least some of the behavior by making several user accounts in your OS, then running multiple instances of Opera, one under each user account, and logging in to opera link with each.

Except they would not share browsing history.

But at least "Facebook dude" would know nothing about "Youtube dude's" cookies.