Firefox sync finally arrived on version 4 release, you can check out instruction on Firefox Sync. It allows you to sync your browser data cross different desktops & mobile devices. You also have the choice of selecting which data you want to sync, and disable others like bookmarks or history.
This is really handy for me as I can sync between my PC at home with my MacBook Pro, even though I mainly use Chrome at home. I have also noticed the performance is much better as well. I will continue to use it for a few days to find out whether it still has the memory issue or not when using it as a tool for web development. The previous versions were all memory hungry when using it at work.
A nice step forward for Firefox.