Multiple browser sessions

I have a program that searches twitter for a product URL then clicks on the URL and adds the product to the shopping cart. I can run multiple instances of my program, but The website only allows 1 item per cart so I'm looking for a way to have my browser open separate windows that are independent so the item doesn't show in the other cart. Thank you.

You should be able to do this by setting up multiple firefox profiles. Setup depends on your OS but plenty of info floating around about this.

I tried that but the problem is the profiles only work if I open the browser under the speicific profile first. The program automatically opens the browser.