Waited four because get how FF otzhiraet memory. When you open many tabs, after the most part closed — the memory consumption is not reduced. In the fourth beta, like it became better, but not completely. Spend an experiment:
1. Work with FF (open/close a bunch of tabs)
2. Leave open two tabs look much eating memory (210 MB)
3. Close FF and choose "save and exit"
4. Start again, open the same tabs
5. Watch memory — 115 MB
What is a joint? I have the feeling there is either a leak or a memory Defrag.