Rabbits get furballs almost as often as cats. The best cure was told to me by a vet years ago. Purchase a pineapple and squeeze some juice from it and give to the rabbit. Some will drink it, others, you may have to put the juice in a syringe to administer. It can't be canned though, it has to be fresh, something about the enzymes in the juice break up the furball.
By Ellen from Ware, MA