Foxmarks has finally picked up where google sync died - password synchronisation.
It's secure, encrypted and so far safe and hassle free. If your not happy with Foxmarks storing your data you have the option to store it elsewhere - if you have the web space and know how to set it up and keep it safe.
I have 3 machines and 5 Firefox installs across windows and Linux installs on each one. Keeping all my site passwords and bookmarks sync'd up is a pleasure. No more having to trying and remember 100's of passwords permunations for all my logins. Do it once, let firefox remember the password and sync foxmarks and it's done.
Some very good speed improvements and ironing out the bugs have madee this one of my favourite plugins. I highly recommend it.