Prior to FB 7.0.13, double-clicking a project item would go through a series of checks to determine if the item was an FB file or one created by another app.
One of those checks was for the antiquated file type/creator attributes.
In FB 7.0.13, type/creator handling was removed entirely.
Unfortunately, this removal means that any files that don't have standard FB extensions will not open in FB when double-clicked in a project window.
This issue has been addressed and the fix will appear in FB 7.0.14.
Bernie