How did you install Seamonkey. I use it myself as my default browser but I've always had trouble when I've installed it with a package manager, the official portage build was awful. I would recommend going to the official seamonkey
site and downloading the source code. Build the app from there and you should get it running well.
I do not know why but I have never had much luck with package manager and Seamonkey, source code has always given me a better result. Let us know how you get on.