A minimal session manager which does exactly what it advertises. A lifesaver when the Firefox built-in session restore forgets a window or three.

The two (Edit: now only one!) small downsides in my opinion are a) the mentioned missing autosave on exit, or autosaving every 30s but only keeping the newest one, and b) that upon session restore it reloads all tabs - unlike the built-in session restore which loads tabs as inactive or unloaded.