CorrectionThe FireFox memory leak, is actual a feature and not a bug. If you want to prevent FireFox from using too much memory, read this article:
Debunking Another Myth FireFox
s Memory Leak Bug.
Some things to improve performance are: use fewer closures, avoid circular references, and when appending DOM elements always append from the document down. There is a lot of information on this issue and the browsers are dramatically improving. However, these three articles cover everything you really need to know: