I don't use SeaMonkey, but I do use Firefox. If I'm reading
correctly, Firefox is but one component of the SeaMonkey
suite, so you'd have to find and uninstall all SeaMonkey
components. It also sounds like SeaMonkey is the default
file association on something. Try checking windows file
associations under control panel, folders, file types.
That should let you know what associations launch SeaMonkey.
You can then change the association to some other program.