Google has just released a terriffic plug-in for Firefox, Google Browser Sync.
In a nutshell, this extension lets you keep your bookmarks, history, cookies and passwords in sync across multiple copies of Firefox. It’s completely configurable (in case you don’t want to give Google access to some of that information, or you just don’t want Doubleclick to track you between multiple browsers), and provides encryption as well. (Unclear whether the encryption keeps Google from data mining my bookmarks.)
Ultimately, I can only give it 5 out of a possible 7 stars because it’s not quite as easy to use as it should be. It relies on a live connection to the server while you browse, so you will get notified if you have one computer connected and fire up Firefox in another. For people (like me) who have multiple computers on their desktop, this can get a bit irritating.
That aside, once you do connect the disconnected Firefox to the sync server, it seems to pick up changes during the interim.
I’ve also had some strange bugs with seriously old cookies replacing the latest versions on my computer. Those seem to have been a one-time problem after my initial sync on all three computers, though.