Hi Hilton,
The short answer is that the browser sends absolutely no information in the request to identify the Tab, or indeed program instance, from which the request comes. So there's no way to do what you want. Such is life.
The root of the issue is the cookie management, which is used to identify the cookie. Memory-cookies (such as used by NetTalk) are shared across tabs, and in some browsers across apparent "instances" of the browser. FF does share, IE doesn't (sometimes.) The one reliable way to open multiple sessions is to use different browsers, one IE, one FF, one Chrome and so on.
That said, there are special cases. For example if you are running Chrome, and you open a new "Incognito" instance of the browser, then it should get its own cookies. But that doesn't mean this behaviour won't change at some point in the future.
Cheers
Bruce