I developed a web app that checks the existing session login for each new page. So, after logging in the first time, the user is shown a dashboard with a list of functions they can access (My Account, etc). When an item is clicked and the application calls the function, it first checks for the existence of login session. If it's not there, then the user is forced back to login screen. However Firefox is deleting the session at some point so when the session is checked for the new function, the user is forced to login again. Chrome, Safari, Edge do not and are fine.

Enhanced tracking is turned off for the site and is shown as an exception. What is happening and how can prevent it?