i have FF Aurora running on Pentium 3 with 500mb of ram. It seems fine. i do not have crashes. I wish i had more RAM. I feel Aurora is for fine tuning, kind of like your final draft and then beta testing is later.
My 3.6 under Ubuntu is now running slower because I installed version 9. The flash player is buggy in 9....I haven't seen a useful update since 3.6. 4,5,6,... there is always something wrong. On windows = same problem 4 and 5 buggy I haven't installed any new one since then.
8 is the release, 9 is the beta, 10 is aurora, 11 is nightly. Whenever a new version comes out, increment everything. Its not hard. The AA has been on nightly for weeks.