The smaller the animal, the greater the height it can fall from, unhurt. All things being equal, the terminal velocity of a falling squirrel is much slower then that of a cat, and both animals are built to take a decent fall as that is what's needed to survive. The supple muscles of cats and squirrels can stand a fair whack. Evenso, they do get hurt in extreme cases.
I am not sure but something which isn't built for jumping like a mouse would be able to fall from any height without serious damage, being a lot lighter than the bigger animals.