I have a website that tracks the session and state of users as they traverse through the site. Several users can "work together" simultaneously. To test this cooperative functionality, I ran multiple Firefox profiles simultaneously on my computer, using Firefox's Profile Manager. After logging in as two users (one on each separate running Firefox instance), one of my Firefox instances still works, while the other one does not seem to track the session. How do I create and run multiple Firefox instances to allow me to test the functionality of such sites? I believe this worked a few months ago. Perhaps this is a new bug? I even tried running normal Firefox and Firefox Extended Support Release simultaneously, but I ran into the same error.