PayPal blocks copy/paste actions in their "change password" form, citing some irrelevant security issues as the reason. That's a load of crap, and they know it -- disabling copy/paste makes it a lot harder to use a decent password generator and a lot easier to screw up your pwd when retyping, especially if it's a long one (as it should be!).
So, here's the quick'n'dirty way to use an externally generated password in your PayPal account: