i have a web based application which has a multicompany option. Thought it would be cool if users could open different companies in different tabs of their browsers - the choice of companies is set in the 'session' variable, which is unfortunately the same across tabs
That won't work. It won't work even if the person uses different instances of the browsers to browse individual companies on the same (your) site. Can you elaborate more about your needs?
Both php and jsp/servlet have excellent session management, so if ur storing it in session then regardless of browser (even if he opens a different browser) its going to identify it as the same person.