User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0 Build ID: 2016030500 Steps to reproduce: I'm using Firefox for many years, but still it surprises me with bad usability now and then: I was closing the last tab with the mouse after I had restarted Firefox (with several tabs open then), but previous session not yet restored. Actual results: Firefox terminated. After starting Firefox again, restore previous session is unavailable 8-( Expected results: When closing the last tab windows (not the Firefox window) Firefox should have warned that it's going to shutdown. Maybe closing the last tab should not be allowed if Firefox cannot run with zero tabs. The last session should be available. As I'm also using GNU Emacs for almost 30 years now (I'm 100% satisfied with its reliability), let me point out that Emacs cannot only restore the last session, but a bunch of the last sessions. Maybe get inspired and add the last n (configurable) sessions to a ring buffer, where the user can decide which session to restore. Should be rather easy to do, but would be a great improvement!