Gotta love Firefox,
I leave tabs open as a reminder of stuff I gotta do (even hibernating my PC with them still open), and the last time and the last time I had to do a proper PC shut down Firefox asked, "Are you sure you want to close 108 tabs?" I didn't realise I had that many open.
There's no way any version of IE or Chrome could have coped with that quantity of open tabs. The CPU would have gone haywire. I guess it helps that I don't overload Firefox with lots of add-ons