Just thought I'd share. I thought it was a handy function, not sure why it was removed. Anyway it can be resurrected easily enough:
Firefox 4 doesn't save tabs (Firefox 5 and Firefox 6)
More bone-fida looking page with solution, but less readable: Firefox 4 doesn't ask me to save a session with mutiple tabs | Firefox Support Forum | Firefox Help
Firefox 4 doesn't save tabs (Firefox 5 and Firefox 6)
More bone-fida looking page with solution, but less readable: Firefox 4 doesn't ask me to save a session with mutiple tabs | Firefox Support Forum | Firefox Help