When linking to an SWF file via the File resource, the SWF does not display in Firefox (Windows or Mac), but does display in Safari and Chrome (both Windows and Mac).
However, when adding the same SWF to a Page resource using the "Moodle Media" button in the HTML editor, the SWF file displays in Firefox as expected.
So I conclude that it's not specifically a Firefox problem, but an issue with the way Moodle is trying to display the SWF file in Firefox via the File resource.
Note, FLV files added to a Moodle page using the File resource works fine in Firefox.
A fix for this will be greatly appreciated.