When I jump between machines, I wish that I had the same experience when it comes to things like: the bookmarks on the machine, and the extensions installed.
I would love to signup for a service that keeps track of my Firefox, and keeps them all in sync on any machine. It can be a plugin itself, and once installed, everything is sync’d.
In fact, I would love a service that tracks ALL preferences that I care about. Soon it would be like being at Sun and putting in your java card to get the same session back, but not running X and such ;)