Using a damp paper towel to gather loose fur off the cage floor works well. The reliable wire brush to get it out of the corners. After grooming with the slicker brush, you can run a damp paper towel over the bunny to pick up stray loose hairs. What did we ever do before paper towels?
When they are molting I feed them a Papaya tablet once or twice a day. The enzyme in the papaya helps break down ingested fur and helps prevent fur block. Papaya is good for their digestive track (for humans too!). I give papaya to the does when they pull fur to line their nestboxes. Actually the rabbits love the papaya tablets so much, they beg for them when you open the bottle. Keen smell. If a rabbit goes off feed, they will often eat papaya tablets before they start eating their grain again. Most of mine eat a tablet right out of my hand. Word of caution, once you start feeding them papaya tablets, they will come to expect them. And some have been known to sulk to get them!