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.