Originally Posted by
CommodusIV
The main distinction between then and now is the Quantum release, which broadly encompasses UI changes, performance improvements, 'chromified' experience in UI and backend performance (behaves more like chrome now, basically), a new platform for addons (makes every older plugin out of date until they use the new system, which has happened by now for any currently maintained plugin) and many bug/security fixes. Nothing so critical that you should act like you're running on windows XP, but the bug and exploit issue is always there, and could bite those who live in the older editions.
That's what I got from comparing between 56 and now, anyways.