They do not have the internal gyroscope to right themselves.
They do not have the twist mechanics in their ankle to maneuver around heights with corners .
They have next to no proprioceptive abilities – judging where they are in relation to themselves and objects in space.
If you see the ferret on something, pick it up and take it off so it doesn’t have to jump off, or have something that can be used as a step down so the ferret doesn’t jump. If you put something as a step down, you will see that a ferret will nearly always use that rather than just jump down. If you have a ferret that climbs a cage, move the cage away from the wall because they nearly always climb by shimmying between the cage and the wall. If the ferret still climbs the cage, you MUST provide a way for the ferret to get down safely – a mountain of bedding beside the cage, a cat tree tilted against the cage (but with a lot of soft stuff underneath in case of a fall), a very thick fleece blanket hanging from the side that the ferret can cling to in order to get down (not really safe), etc. The best option is to consider getting a smaller cage since this is always going to be a big risk to the ferret.
If you have a tall cat tree for your cats or the ferrets, have soft things, like small bean bag chairs, around the tree in case of a fall. It will happen at some point and the ferret can be seriously injured.