Remember that nasty dialog that appears when you start Firefox?
"Your last Firefox session closed unexpectedly... " with 2 buttons: "Restore session" and "Start New Session".
Well, simply put, that's just stupid. That's just extra excise - and besides, why do I need to bother remembering what tabs I had opened? This appears even when I click some link from another application (like, Thunderbird), and Firefox is not opened yet.
But more to the point, I can end up clicking "Start New Session", and have all my previous tabs lost.
First of all, Firefox should not ask that stupid question, and by default start with no tabs. It should then keep a history of the last 10 "Tab Groups", so that in case you want to re-open any of those tabs, you could. You should be able to re-open a full Tab Group, or select some tabs from a Tab Group and open only those.