Many websites use session-cookies (PHP session installs such a cookie, for example). Session-cookies have expiry time of zero, and the browser usually deletes them after closing its window. This is very useful for a 'log-in' session, like in your bank account, gmail, etc.

So all browsers delete the cookie as you close them, but what happens when you open a new browser window or tab? Does it also respect this temporary, session cookie? If you're logged in to gmail from one window, can you open a new browser window with another gmail account?

The answer is not surprising: that depends on your browser.

According to this article:

• Firefox would always respect the session cookie, whether it's a new window or tab.
• IE would respect the session in all tabs/windows running in the same IE process:
  • Tabs, pop-ups and Ctrl+N (File -> New) windows are running in the same process, thus would respect the session-cookie.
  • Re-running iexplore.exe (either from the desktop/launch pad/start menu) would create a separate process, unaware of the session cookies from the other IE process.

  Funny thing is that if you have less than 32MB ram, even re-running iexplore.exe wouldn't create a separate process, on IE 6.0 and earlier.