This URL filtering requires you to specify your choices in the custom display settings. The important part you are missing is adding a row to the "where" section. If you use "?fieldkey=value", then you would add a where row to set that field "equal to" "[get-fieldkey]". In the bugs example, "Where" is set to: Status is equal to [get-status].
Let me know if that doesn't help.
P.S. You'll get faster support if you post in the Pro forums.