I've got a bunch of SNES roms in archives that are stored with the .sfc file extension inside the archive. When I try to open these, OpenEmu doesn't know what to do. If I unzip the ROMs and rename them to .smc OpenEMU fires up BSNES or SNES9X just fine. It would be nice if it would just do that for .sfc though :)
IIRC there's also "raw SNES" formats and Front Fareast. I can't remember the extensions.
In either case they just need to be added to Info.plist.
I can verify this bug with openemu 1.0.0b6 on 10.6.5.
After adding an sfc entry to CFBundleTypeExtensions within info.plist as mrvacbob suggests, files ending in sfc are no longer grayed out when using the File>Open window. However, opening any SNES roms ending in sfc has no result (no crash or errors, nothing happens), even though the same file renamed to end in smc works fine.