The default browser architecture allows a web-user to only share a single session of a particular domain.
Precisely, if you login to your Gmail account in one tab & tried to login to another GMail account in another tab or in new browser window, you’ll be automatically redirected to your previously logged in GMail account. This happens because of the concept called “Session Cookies”.
In short, what will you do to log in to your multiple GMail/Yahoo!/Hotmail account at the same time. As a quick heal, web-guys uses “InPrivate” mode (a.k.a. Porn mode) in IE8 or use their secondary browser. Clearly, that appears to be simple & perfect.
Strangely, IE8 has a new feature called “New Session”, solely to meet the above mentioned requirement.
When you click on the “New Session”, a new browser window starts. This browser window will not share the session cookies with the original browser window. Hence, you can login to your multiple account, simultaneously.