Description of problem: It is quite clear that seamonkey build process assumes that gnome-vfs2 is available but a line BuildRequires: gnome-vfs2-devel is missing from a spec file. It appears also that BuildRequires: libXrender-devel BuildRequires: krb5-devel would not be out of order. Version-Release number of selected component (if applicable): seamonkey-1.0.4-0.5.1.fc5 (and likely others too).
This is fixed in seamonkey-1.0.5-0.5.fc5 and in SeaMonkey for FC6.