From FDT Documentation
FDT's Quick Explore is a feature that was added in FDT 4.3. It enables you to have FDT quickly reveal the selected file or folder in your operating systems explorer.
To use Quick Explore, select the item in the Flash Explorer and either Right Click > Quick Explore or use the default key stroke CMD+4.
The default key stoke can be changed anytime via FDT's preferences (see below).