Comment 3 for bug 105474

It seems to be permission related for both ntfs-3g and fat32. If you mount NTFS without the use of any of uid, gid, umask, fmask and dmask options, i.e. no permission checking is done at all, then probably download will work. Otherwise you must configure these options in a way that the relevant firefox user permissions match the preconfigured NTFS one, even if you use the 'silent' option.

On fat32 the quiet option may help.