Firefox problem with Cappuccino

Today I played with Cappuccino and encountered a quirk with Firefox

• If the app is accessed via http://, it works, but the debug console shows that Firefox attempts to fetch Frameworks/AppKit/AppKit.j and Frameworks/Foundation/Foundation.j, and of course gets 404.
• If the app is accessed via file://, it stops at the loading screen with the spinning indicator. The debug console shows Firefox complains about not finding some AppKit/Foundation classes in search paths.

UPDATED: Other browsers on Mac work normally (Safari, Opera, Chrome, OmniWeb) except for Camino and Flock, so I guess this has something to do with the Gecko engine.