3.6.x has been known for generally being more stable and using less RAM than the modern Firefox 10...
I actually don't agree with your premise. While Firefox had some issues around version 4, Firefox 10 is actually faster and more stable than Firefox 3.6 was, and RAM usage is on a downward trend. I understand that Firefox ~4 turned you off because I was really irritated by the regressions that came around that time, but things *did* get better. If you give it another try and make sure you give it a fair shake without already having decided it's worse, I think you'll find it's actually an improvement over what you're using right now. It's not like Firefox 3.6 was a speed demon in its day either... Firefox's memory hog problems go back way further than that.
"The one charm of marriage is that it makes a life of deception a neccessity." - Oscar Wilde