140541 unlimited sessions in browser

I need to have multiple or unlimited sessions opened in a web browser. It would be great that it was Mozilla Firefox. The idea is that my client has multiple users on the same dating site, and when he signs in with one user, he cannot sign in with a second one, only if he uses a different browser. I would need this: 1. The possibility of having as many sessions (users) connected at the same time on the same browser, we don't use IE7) 2. The possibility of having all users connected in different sessions without any tabs on the browser. 3. When I start the browser, have bookmark maybe that when clicked it connects to site automatically with all users and passwords, so that all users are online at the same time and seen by other users. We have like 20-40 users and we'll have more, so we want the users to be online all the time so that they are seen on that site. If we have a browser with 40 tabs or more, it's just too much. I need a solution for this, do you have any in your mind?