"extreme" browsers like me. I run anywhere from 30 to 150 tabs open at a time. I'd say a nice average would be around 60 tabs
As much as I appreciate the EFF's efforts, I wound up disabling 4.0. Maybe 4.0.1 will be back with a vengeance.
Anyway, Firefox wasn't crashing, it was slow. Probably one of your in-profile databases got corrupted at some point ('restore from backup' is the most likely "fix"). I'm on Fedora 20, running stock Firefox.