A user interface control for scrolling a display of computer program data during retrieval of computer program data includes a scrollable data retrieval progress indicator. The scrollable data retrieval progress indicator includes a track with a length that indicates the total amount of the computer program data being retrieved, an extendable scrollbar overlying the track with a variable length that extends within the track as the computer program data is received and indicates, in combination with the length of the track, a ratio of available scrollable received computer program data to a total amount of the computer program data being retrieved, and a thumb button overlying the extendable scrollbar and movable within the variable length of the extendable scrollbar to scroll the available scrollable received computer program data.