Dorian,
You cannot select a file to open from the Browse Folders window. This window is just for navigating to the folder containing the file(s) you wish to load, and you will notice that the file names are grayed-out and cannot be selected.
Having browsed to the desired folder, you then close this window and select the file(s) to load from the Load Dictation Files window. Only files with a format supported by Express Scribe will be displayed. On the Mac these will be wav, mp3, dct, and aiff files.
nchpm