FormsAuthentication Uses The Same Ticket Throughout Browsers (on the same PC)?

I do not understand what's going on with FormsAuthentication. When I first turn on my PC and start working on my project, everytime I try to login, I get an error telling me that the queried username (nickname in my case) is not found the sequence. I check its value while debugging, it turns out it's a null string (""). Then if I stop debugging then start it again, I get logged in normally and it picks up the right username. Moreover, if I try to login with another user from another browser, the same thing happens but eventually it picks up the same user that was logged in using the same browser! Does FormsAuthentication use the same ticket in all browsers, for all users? Is there anything I can do about it? Or could it be that I'm doing something wrong here...? Here's my code: [HttpPost] public ActionResult Login(LoginViewModel dto) { bool flag = false; if (ModelState.IsValid) { if (_userServi ...