To prevent hairballs, brush or comb your rabbit everyday when it is going through a heavy shed/molt.
If the rabbit does get a hairball, it will not look bloated but may stop eating or eat very little. If your rabbit stops eating it can mean a number of things. However, if it has been violently molting then treat for a hairball.
To break down the hairball and get the gut moving properly, give the rabbit a couple papaya enzymes. They can be purchased at any vitamin store.
After the hairball is nonexistent, increase the playtime of your rabbit and give it more exercise. Rabbits that are fit and healthy should never get a hairball.