In IE8 and above, you can open multiple instances of this browser by running it with the -nomerge . This way, the session cookie will be separate for each instance. (source: IEBlog )
There are several ways for Firefox to achieve the same result as here on SuperUser
Chrome / Chromium and Opera have a private mode in which session cookies are not shared with other windows of the same browser (create a private window with Ctrl + Shift + N )
Tested in all of the above; note that this is universally valid only for session files (those that expire when the browser closes) - persistent cookies are processed slightly differently in each browser.
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