I had the same problem but was able to solve it. I downloaded the
lasted version of seamonkey from mozilla. I then extracted the zip
file and used the setup inside. It tries to install to user,but gives
you the option to change thedestination. Change It to your home
folder. It will install it there. The addons and theemes will install
from mozilla ok.I had some problems with plugins but solved that by
going to User/lib/firefox/plugins. Copy and paste what you want into
your seamonkey/ plugins folder. Worked for me. You will have to update
from mozilla.