Changes

During a browsing session, Firefox writes the session data whenever any tabs are changed; opening/closing a tab, going to another page in a tab, or going back/forward in the tab's history are all triggers that result in the session being saved. When a session is saved, the list of open tabs and each history entry within those tabs are iterated, serialized to JSON, and written to sessionstore.js in the profile.  Rather than writing state to the disk, most Android apps usually write state to the activity's bundle in onPause(). However, writing the session to disk guarantees that the session can still be recovered after a crash, whereas the bundle is only alive after the app has been gracefully killed in the background by the OS.