1. A method comprising: from a collection of media objects, establishing a current set of media objects; concurrently displaying a first plurality of single-action controls; wherein each single-action control of the first plurality of single-action controls corresponds to a filter option; wherein selection of any single-action control, of the first plurality of single-action controls, automatically causes the current set of media objects to be filtered based on the filter option that corresponds to the single-action control that was selected; in response to selection of a particular single-action control of the first plurality of single-action controls, changing which single-action controls are displayed based on which media objects remain after filtering the current set of media objects based on the filter option that corresponds to the particular single-action control, by performing the steps of: filtering the current set of media objects, based on the filter option associated with the particular single-action control, to produce a filtered set of media objects; for at least one hierarchical dimension, performing the steps of determining how many distinct values the media objects in the filtered set of media objects have at each level of the hierarchical dimension; selecting a particular level of the hierarchical dimension as the display level for the hierarchical dimension based, at least in part, on how many distinct values the media objects in the filtered set of media objects have at each level of the hierarchical dimension; and displaying a second plurality of single-action controls, wherein each single-action control in the second plurality of single-action controls corresponds to a filter option for a respective one of the distinct values the media objects in the filtered set of media objects have at the display level of the hierarchical dimension; wherein selection of any single-action control, of the second plurality of single-action controls, automatically causes the filtered set of media objects to be filtered based on the filter option that corresponds to the single-action control that was selected; wherein the method is performed by a mobile device executing a media object navigation tool.